latest try at backward/northamerica fix

[Paul Eggert]

Arthur David Olson <olsona at elsie.nci.nih.gov> writes:

> Here's my lastest try at avoiding problems with zones such as CST5CDT;

The patch to 'backward' looks fine, but the patch to 'northamerica'
has some problems.  First, it removes support for TZ='EST', TZ='MST',
TZ='HST', which have been in the tz database since 1987.  Second, it
creates new Zones AST4ADT, YST9YDT, HST10HDT that are not needed for
backwards compatibility, as they have never been supported by the tz
data.  Third, it creates new Zones AST4, EST5, CST6, MST7, PST8, YST9,
HST10 that also are not needed for backward compatibility (for the
same reason as above), and furthermore don't change how TZ strings are
evaluated (as they are equivalent to their POSIX interpretations).

Here's a proposed patch to 'northamerica' to address these issues.

--- northamerica	2005/11/28 15:52:28	2005.15
+++ northamerica	2005/12/19 21:52:52	2005.15.1.2
@@ -131,6 +131,24 @@ Rule	US	1987	2006	-	Apr	Sun>=1	2:00	1:00
 Rule	US	2007	max	-	Mar	Sun>=8	2:00	1:00	D
 Rule	US	2007	max	-	Nov	Sun>=1	2:00	0	S
 
+# From Arthur David Olson, 2005-12-19
+# We generate the files specified below to guard against old files with
+# obsolete information being left in the time zone binary directory.
+# We do these as separate Zones rather than as Links to avoid problems if
+# a particular place changes whether it observes DST.
+# We put these specifications here in the northamerica file both to
+# increase the chances that they'll actually get compiled and to
+# avoid the need to duplicate the US rules in another file.
+
+# Zone	NAME		GMTOFF	RULES	FORMAT	[UNTIL]
+Zone	EST		 -5:00	-	EST
+Zone	MST		 -7:00	-	MST
+Zone	HST		-10:00	-	HST
+Zone	EST5EDT		 -5:00	US	E%sT
+Zone	CST6CDT		 -6:00	US	C%sT
+Zone	MST7MDT		 -7:00	US	M%sT
+Zone	PST8PDT		 -8:00	US	P%sT
+
 # From Bob Devine (1988-01-28):
 # ...Alaska (and Hawaii) had the timezone names changed in 1967.
 #    old			 new