timezone configuration patch

[Michael M Slusarz]

All,
Yet another hack from me :)  This time I grew tired of waiting for a timezone 
drop-down menu implementation to be done so I did it myself.

Diffs/new files/pictures of the hack in action can be found at:
http://bigworm.colorado.edu/imp-patches/timezone.php

A few things I discovered while putting it together:

1. A string of the form [+-]0200 ([+-]hours difference from GMT) does NOT 
appear to work at all.  I'm using a Linux system, and if you put anything in 
this form and send a message it appears that whatever is using the TZ 
environment variable (sendmail/postfix/qmail ??) will just ignore it and your 
message will be sent with time -0000 GMT.

2. This is because the correct POSIX.1 TZ implementation is:
  STDoffset[DST[offset], (some other stuff...)]
  where STD is the 3+ letter code for the time zone and
  where DST is the 3+ letter code for the daylight time zone

  Thus, the TZ variable must be something as follows:
    EST5EDT
    MST7MDT
    etc.

  This works fine for american timezones, but it turns out there is no 
convention for worldwide timezone abbreviations, etc.  Additionally, half-hour 
deviations do not seem to work well.  If you try IT-3:30 (Iran - 3hr 30min.), 
it will say your mail message came from about a month ago and stuff.  Plus, the 
default DST rules are americanized and may not be correct for the rest of 
world - and most likely isn't.  Yuck.

3. Luckily, there is the POSIX.1 extensions of Country/City which handles all 
of these problems.  This convention handles all of the peculiarities that occur 
in the same time zones (i.e. there are about 3-4 different time zone rules in 
the state of Indiana alone).  This is the way I have implemented my patch.  A 
nice thorough list of Country/City combinations can be downloaded from 
ftp://elsie.nci.nih.gov/pub/.  These are the timezone codes used by GNU/glibc 
based systems.  The only drawback is that I don't know if this will work on a 
non GNU-like system (i.e Windows, Solaris).  But this is as good as I think it 
can get without implementing an entire timezone system in PHP.

The patch allows you to lock the timezone and set a default timezone (using the 
normal syntax in imp/config/prefs.php).

Let me know if you have any questions/comments.

michael

_______________________________________________
Michael Slusarz [slusarz@bigworm.colorado.edu]
The University of Colorado at Boulder