"date_timezone_set" override the TZ environment variable, which on its turn
overrides the date.timezone setting. If none of the three is set, we fallback
to UTC.
- Added "date_timezone_set" function to set the timezone that the date
functions will use.
- Removed old date/gmdate implementations.
- Moved date() related testcases to ext/date/tests.
- Implemented bug #33452.
- Fixed testcase for bug #27719 - there is no timezone called "EST5DST".