Improve time zone documentation

* doc/lispref/os.texi (Time Zone Rules):
New section, mostly with material moved here from other sections.
* doc/emacs/cmdargs.texi (General Variables):
* doc/lispref/os.texi (Time Conversion, Time Parsing):
Xref new section.
* etc/NEWS, etc/PROBLEMS:
* lisp/org/org.el (org-timestamp-format):
* src/editfns.c (Fformat_time_string, Fdecode_time)
(Fencode_time, Fcurrent_time_string, Fcurrent_time_zone)
(Fset_time_zone_rule):
When documenting time zone rule strings, mention the TZ
environment variable in preference to mentioning the
sort-of-internal function set-time-zone-rule.

1 files changed, 4 insertions, 4 deletions

diff --git a/etc/PROBLEMS b/etc/PROBLEMS
index b0c21ee25dd..be9400bf264 100644
--- a/etc/PROBLEMS
+++ b/etc/PROBLEMS
@@ -2220,11 +2220,11 @@ month names with consistent widths for some locales on some versions
 of Windows.  This is caused by a deficiency in the underlying system
 library function.
 
-** Problems with set-time-zone-rule function
+** Non-US time zones.
 
-The function set-time-zone-rule gives incorrect results for many
-non-US timezones.  This is due to over-simplistic handling of
-daylight savings switchovers by the Windows libraries.
+Many non-US time zones are implemented incorrectly.  This is due to
+over-simplistic handling of daylight savings switchovers by the
+Windows libraries.
 
 ** Files larger than 4GB report wrong size in a 32-bit Windows build