[Zope] DateTime.py patch

[Shane Hathaway]

Zope fans,

I have just done a line-by-line audit of DateTime.py.  There were a
number of issues, some of which have been submitted to the collector. 
I have corrected everything I could find.

Gregor Hoffleit recently submitted a patch for DateTime.py as well.  He
made some of the same corrections I did, though in a different way.

The major changes are:

- Usage of integer arithmetic where possible to eliminate rounding
errors.
- Better support for daylight savings time.
- Usage of long integer milliseconds, making it possible to do date
comparisons with more predictable results.
- Date comparisons are now time zone independent, meaning that a
DateTime set to 3:00 PM in GMT-5 is equivalent to a DateTime set to
4:00 PM in GMT-4.

If do any work with Zope's DateTime or have had any issues with it,
please install this patch so it can be fully tested.  I have already
tested it to the best of my ability.  I expect this to become part of
the main distribution once it has been tested.

http://www.zope.org/Members/hathawsh/DateTime.py

There is one change made by Gregor which I feel I could not
incorporate.  Gregor added the "CET" and "CEST" time zones to the list
of recognized time zones.  Rather than add it now, I would prefer to
get a complete list of zones which are not included (EDT, which happens
to be the time zone I am in right now, is also missing.)  For now,
those zones should be correctly translated to GMT offsets.

On a slightly different note: Recently there was a thread that
described a problem with the time format of Z2.log.  That problem is
unrelated to DateTime.py.  ZServer/medusa/http_server is written
incorrectly; where it accesses gmtime() it ought to be calling
localtime().  Also, it needs to be updated for daylight savings time
the same way DateTime was.

Shane