* Fixed the issue of all date functions throwing E_STRICT on their first call due...

* Fixed the issue of all date functions throwing E_STRICT on their first call due to the default timezone not being set. Used the same approach as phpMyAdmin: utilise PHP's server timezone detection code (which unconditionally throws E_STRICT) with warnings disabled, and store the result with date_default_timezone_set() to avoid future notices. Avoids the need for warning suppression to be dotted all over the codebase, like r58559.
* (bug 2658) Don't use the TZ environment variable at all. Setting it throws an error in some restricted setups. But using it in PHP 5.1+ doesn't make sense anyway, since you'll get the E_STRICT notice described above whenever PHP tries to access it, because Derick hates environment variables. Use date_default_timezone_set().
* If $wgLocaltimezone is null, use the server's timezone as the default for signatures. This was always the behaviour documented in DefaultSettings.php but has not been the actual behaviour for some time: instead, UTC was used by default.