[tz] suggestion: split "backward" into "backward" and "deprecated"

[Andrew Gierth]

In a post on this list on Nov 24 last, Garret Wollman said regarding
FreeBSD's c.1994 change (now reversed) to not install "backward":

 >> I chose not to install the "backward" zones in the hope that this
 >> would more securely deprecate the then-recently-obsoleted old-style
 >> names like "US/Eastern", and then maybe they could be completely
 >> removed from the distribution if other downstream consumers (only a
 >> few operating systems at that point, no language runtimes) would do
 >> likewise.

 >> Unfortunately, these ancient compatibility links never got deleted,
 >> so "backward" now contains a mix of ancient and more recent
 >> compatibility links, and users are still using them (or being told
 >> to use them by documentation that should have been updated decades
 >> ago).

The obvious way to resolve this would be to split "backward" into two:
one file containing aliases that were once regarded as canonical names
(or at least names consistent with current naming theory) but were then
renamed (e.g. the recent example of Godthab -> Nuuk), the other
containing all the ancient stuff that never conformed to the current
style (such as "W-SU", "Poland", "GB-Eire", "US/Eastern" etc.).

One way to do this might be to set a cutoff date, for which the 2000a
data release seems like a good choice, and retain only the zones changed
since then in "backward", moving the remainder to a new "deprecated"
category.

Another way would be to reserve "backward" for zones that have appeared
in zone.tab at any time, and move the rest to "deprecated".

It turns out that these two methods give almost exactly the same
results, with only two exceptions: America/Ensenada was in "backward"
before 2000 going by the SCM history, but existed in zone.tab until
2010; and Asia/Ulan_Bator was added to "backward" and removed from
zone.tab in the 2000a release. This suggests that the zone.tab criterion
is a slightly better one.

(One further exception should be made: the link from Etc/UTC to UTC is
in widespread use and should probably be moved to "etcetera" alongside
the similar "GMT" link. Otherwise it should stay in "backward". This
change already exists in FreeBSD, where all "GMT" defaults have been
changed to "UTC" at some point.)

Split this way, the list of links in "backward" would become (posted in
plain text here for readability, I can submit in patch form if needed)
as follows:

Link    Africa/Nairobi          Africa/Asmera
Link    Africa/Abidjan          Africa/Timbuktu
Link    America/Argentina/Catamarca     America/Argentina/ComodRivadavia
Link    America/Argentina/Buenos_Aires  America/Buenos_Aires
Link    America/Argentina/Catamarca     America/Catamarca
Link    America/Atikokan        America/Coral_Harbour
Link    America/Argentina/Cordoba       America/Cordoba
Link    America/Tijuana         America/Ensenada
Link    America/Nuuk            America/Godthab
Link    America/Indiana/Indianapolis    America/Indianapolis
Link    America/Argentina/Jujuy America/Jujuy
Link    America/Kentucky/Louisville     America/Louisville
Link    America/Argentina/Mendoza       America/Mendoza
Link    America/Toronto         America/Montreal
Link    America/Rio_Branco      America/Porto_Acre
Link    America/Argentina/Cordoba       America/Rosario
Link    America/Tijuana         America/Santa_Isabel
Link    America/Denver          America/Shiprock
Link    Pacific/Auckland        Antarctica/South_Pole
Link    Asia/Ashgabat           Asia/Ashkhabad
Link    Asia/Kolkata            Asia/Calcutta
Link    Asia/Shanghai           Asia/Chongqing
Link    Asia/Shanghai           Asia/Chungking
Link    Asia/Dhaka              Asia/Dacca
Link    Asia/Shanghai           Asia/Harbin
Link    Asia/Urumqi             Asia/Kashgar
Link    Asia/Kathmandu          Asia/Katmandu
Link    Asia/Macau              Asia/Macao
Link    Asia/Yangon             Asia/Rangoon
Link    Asia/Ho_Chi_Minh        Asia/Saigon
Link    Asia/Thimphu            Asia/Thimbu
Link    Asia/Makassar           Asia/Ujung_Pandang
Link    Asia/Ulaanbaatar        Asia/Ulan_Bator
Link    Atlantic/Faroe          Atlantic/Faeroe
Link    Europe/Oslo             Atlantic/Jan_Mayen
Link    Etc/UTC                 Etc/UCT
Link    Europe/London           Europe/Belfast
Link    Europe/Chisinau         Europe/Tiraspol
Link    Pacific/Honolulu        Pacific/Johnston
Link    Pacific/Pohnpei         Pacific/Ponape
Link    Pacific/Chuuk           Pacific/Truk
Link    Pacific/Chuuk           Pacific/Yap
Link    Etc/UTC                 UTC

"deprecated" would contain these links:

Link    America/Adak            America/Atka
Link    America/Indiana/Indianapolis    America/Fort_Wayne
Link    America/Indiana/Knox    America/Knox_IN
Link    America/Port_of_Spain   America/Virgin
Link    Asia/Jerusalem          Asia/Tel_Aviv
Link    Australia/Sydney        Australia/ACT
Link    Australia/Sydney        Australia/Canberra
Link    Australia/Lord_Howe     Australia/LHI
Link    Australia/Sydney        Australia/NSW
Link    Australia/Darwin        Australia/North
Link    Australia/Brisbane      Australia/Queensland
Link    Australia/Adelaide      Australia/South
Link    Australia/Hobart        Australia/Tasmania
Link    Australia/Melbourne     Australia/Victoria
Link    Australia/Perth         Australia/West
Link    Australia/Broken_Hill   Australia/Yancowinna
Link    America/Rio_Branco      Brazil/Acre
Link    America/Noronha         Brazil/DeNoronha
Link    America/Sao_Paulo       Brazil/East
Link    America/Manaus          Brazil/West
Link    America/Halifax         Canada/Atlantic
Link    America/Winnipeg        Canada/Central
Link    America/Toronto         Canada/Eastern
Link    America/Edmonton        Canada/Mountain
Link    America/St_Johns        Canada/Newfoundland
Link    America/Vancouver       Canada/Pacific
Link    America/Regina          Canada/Saskatchewan
Link    America/Whitehorse      Canada/Yukon
Link    America/Santiago        Chile/Continental
Link    Pacific/Easter          Chile/EasterIsland
Link    America/Havana          Cuba
Link    Africa/Cairo            Egypt
Link    Europe/Dublin           Eire
Link    Europe/London           GB
Link    Europe/London           GB-Eire
Link    Etc/GMT                 GMT+0
Link    Etc/GMT                 GMT-0
Link    Etc/GMT                 GMT0
Link    Etc/GMT                 Greenwich
Link    Asia/Hong_Kong          Hongkong
Link    Atlantic/Reykjavik      Iceland
Link    Asia/Tehran             Iran
Link    Asia/Jerusalem          Israel
Link    America/Jamaica         Jamaica
Link    Asia/Tokyo              Japan
Link    Pacific/Kwajalein       Kwajalein
Link    Africa/Tripoli          Libya
Link    America/Tijuana         Mexico/BajaNorte
Link    America/Mazatlan        Mexico/BajaSur
Link    America/Mexico_City     Mexico/General
Link    Pacific/Auckland        NZ
Link    Pacific/Chatham         NZ-CHAT
Link    America/Denver          Navajo
Link    Asia/Shanghai           PRC
Link    Pacific/Pago_Pago       Pacific/Samoa
Link    Europe/Warsaw           Poland
Link    Europe/Lisbon           Portugal
Link    Asia/Taipei             ROC
Link    Asia/Seoul              ROK
Link    Asia/Singapore          Singapore
Link    Europe/Istanbul         Turkey
Link    Etc/UTC                 UCT
Link    America/Anchorage       US/Alaska
Link    America/Adak            US/Aleutian
Link    America/Phoenix         US/Arizona
Link    America/Chicago         US/Central
Link    America/Indiana/Indianapolis    US/East-Indiana
Link    America/New_York        US/Eastern
Link    Pacific/Honolulu        US/Hawaii
Link    America/Indiana/Knox    US/Indiana-Starke
Link    America/Detroit         US/Michigan
Link    America/Denver          US/Mountain
Link    America/Los_Angeles     US/Pacific
Link    Pacific/Pago_Pago       US/Samoa
Link    Etc/UTC                 Universal
Link    Europe/Moscow           W-SU
Link    Etc/UTC                 Zulu

-- 
Andrew.