torbutton_set_timezone() does not work (properly)

While implementing the normalization of the timezone (thanks for the idea Mike) I figured out that the function is not working (properly) in Torbutton currently. Maybe that is intentionally as I have not looked at the Torbutton code thoroughly. In this case just ignore my comments and close this ticket as invalid (or whatever). There are two points to raise:

1. The original timezone is not saved in the preferences, I get always a UTC+00:00 which could be bad if the user is toggling the anon mode (I know toggling is dead but the option is still available buried in the preferences).

2. The code in the function does not cope with timezones like GMT-3:30 as Math.floor() gives wrong values back (in this case "-6" instead of "-5").