win32 timezone map

Per discussion off-list with Tom, here is a patch to redo the way the
system timezone is detected on win32. Instead of trying to figure out
what to do, it just looks in a lookup table for all available timezones
(there is a finite and stable number of timezones on a win32 system,
unlike unixes that can have timezones added manually in most cases).

I've tried to match the timezones as good as I could using the city
names from the win32 descriptions and using some google. There are
probably some that can have better mappings - local knowledge is
probably the key there.

In passing the patch also removes some of the kludges put in the tz
detection code that were specific for win32.

//Magnus