First pass at 'fixing' timezones.

Currently timezones are internally hardcoded as 'Europe/London'
(this is what I care about of course ;) ) it will be possible
to specify the *server* timezone in the future.  For now though,
tests should now work wherever as they'll generate the correct
GMT/UTC based unix timestamps properly now.
Merge pull request #14 from ciaranj/fix_timezone_shenanigans

First pass at 'fixing' timezones.