Time zone difference now specified relative to the server's time instead of relative...

Time zone difference now specified relative to the server's time instead of relative to GMT. As Jeff pointed out, by using a time relative to the server, sometimes the time would remain correct when daylight savings starts / stops, dependant upon the time zones involved. (Otherwise we'd have to open up a new can of worms by fully implementing all the named time zones, each with differing daylight savings time rules.)

git-svn-id: svn://svn.code.sf.net/p/phpwiki/code/trunk@1913 96ab9672-09ca-45d6-a79d-3d69d39ca109