Standard for timezone handling with TZ

[Paul Eggert]

I very much like the idea of putting the GMT+-nnnn time zones into an
Etc subdirectory; I think this clarifies things.

I think it would clarify things further if all the etcetera zones and
links were put into the Etc directory; we can use `backward' to bring
the important ones back to the top level.

Since the signs are changed, we now want GMT-13, not GMT+13.

The etcetera comments are a bit terse for people who don't know the
notation well.

Finally, I noticed that `backward' contains Moscow out of order; since
`Moscow' was never used before late 1993, we can remove it.

So I propose the following changes.

===================================================================
RCS file: RCS/etcetera,v
retrieving revision 7.2
retrieving revision 7.2.1.1
diff -c -r7.2 -r7.2.1.1
*** etcetera	1994/02/22 23:03:36	7.2
--- etcetera	1994/02/22 23:43:36	7.2.1.1
***************
*** 4,28 ****
  # that's right for their area, even if it doesn't have a name or DST rules
  # (half hour zones are too much to bother with -- when someone asks!)
  
- Zone	GMT		0	-	GMT
- Link	GMT		UTC
- Link	GMT		UCT
- Link	GMT		Universal
- Link	GMT		Greenwich
- Link	GMT		Zulu
- Link	GMT		GMT-0
- Link	GMT		GMT+0
- Link	GMT		GMT0
- 
  # We use POSIX-style signedness in the names and output,
  # internal-style signedness in the specifications.
! # These are shoved down into an "Etc" directory so we get a name change--
! # in earlier incarnations, we had lines such as
  #		Zone	GMT-12		-12	-	GMT-1200
! # and do not want things to change quietly if someone accustomed to the old
  # way does a
  #		zic -l GMT-12
  
  Zone	Etc/GMT-12	12	-	GMT-12
  Zone	Etc/GMT-11	11	-	GMT-11
  Zone	Etc/GMT-10	10	-	GMT-10
--- 4,23 ----
  # that's right for their area, even if it doesn't have a name or DST rules
  # (half hour zones are too much to bother with -- when someone asks!)
  
  # We use POSIX-style signedness in the names and output,
  # internal-style signedness in the specifications.
! # For example, TZ=Etc/GMT+4 corresponds to 4 hours _behind_ GMT;
! # it is equivalent to TZ=GMT+4, which is implemented directly as per Posix.
! 
! # Earlier incarnations of this package were not Posix-compliant,
! # and had lines such as
  #		Zone	GMT-12		-12	-	GMT-1200
! # We did not want things to change quietly if someone accustomed to the old
  # way does a
  #		zic -l GMT-12
+ # so we moved the names into the Etc subdirectory.
  
+ Zone	Etc/GMT-13	13	-	GMT-13 # 12 hours ahead of GMT, plus DST
  Zone	Etc/GMT-12	12	-	GMT-12
  Zone	Etc/GMT-11	11	-	GMT-11
  Zone	Etc/GMT-10	10	-	GMT-10
***************
*** 35,40 ****
--- 30,36 ----
  Zone	Etc/GMT-3	3	-	GMT-3
  Zone	Etc/GMT-2	2	-	GMT-2
  Zone	Etc/GMT-1	1	-	GMT-1
+ Zone	Etc/GMT		0	-	GMT
  Zone	Etc/GMT+1	-1	-	GMT+1
  Zone	Etc/GMT+2	-2	-	GMT+2
  Zone	Etc/GMT+3	-3	-	GMT+3
***************
*** 47,50 ****
  Zone	Etc/GMT+10	-10	-	GMT+10
  Zone	Etc/GMT+11	-11	-	GMT+11
  Zone	Etc/GMT+12	-12	-	GMT+12
! Zone	Etc/GMT+13	-13	-	GMT+13	# GMT offset 12 hours with DST
--- 43,54 ----
  Zone	Etc/GMT+10	-10	-	GMT+10
  Zone	Etc/GMT+11	-11	-	GMT+11
  Zone	Etc/GMT+12	-12	-	GMT+12
! 
! Link	Etc/GMT		Etc/GMT-0
! Link	Etc/GMT		Etc/GMT+0
! Link	Etc/GMT		Etc/GMT0
! Link	Etc/GMT		Etc/Greenwich
! Link	Etc/GMT		Etc/UCT
! Link	Etc/GMT		Etc/UTC
! Link	Etc/GMT		Etc/Universal
! Link	Etc/GMT		Etc/Zulu
===================================================================
RCS file: RCS/backward,v
retrieving revision 7.4
retrieving revision 7.4.1.1
diff -c -r7.4 -r7.4.1.1
*** backward	1994/02/07 14:57:49	7.4
--- backward	1994/02/22 23:43:36	7.4.1.1
***************
*** 32,38 ****
  Link	Africa/Cairo		Egypt
  Link	Europe/Dublin		Eire
  Link	Europe/London		GB
! Link	Europe/Moscow		Moscow
  Link	Asia/Hong_Kong		Hongkong
  Link	Atlantic/Reykjavik	Iceland
  Link	Asia/Tehran		Iran
--- 32,39 ----
  Link	Africa/Cairo		Egypt
  Link	Europe/Dublin		Eire
  Link	Europe/London		GB
! Link	Etc/GMT			GMT
! Link	Etc/GMT			Greenwich
  Link	Asia/Hong_Kong		Hongkong
  Link	Atlantic/Reykjavik	Iceland
  Link	Asia/Tehran		Iran
***************
*** 65,67 ****
--- 66,70 ----
  Link	America/Denver		US/Mountain
  Link	America/Los_Angeles	US/Pacific
  Link	Pacific/Samoa		US/Samoa
+ Link	Etc/GMT			UTC
+ Link	Etc/GMT			Universal