`timezone` variable contains the difference, in seconds, between UTC and
local standard time (see `man 3 localtime` on Solaris).

Call to `tzset` is required to apply contents of `TZ` variable to
`timezone` variable.

BUG=v8:2064

Review URL: https://chromiumcodereview.appspot.com/10967066
Patch from Maciej Małecki <me@mmalecki.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@12802 ce2b1a6d-e550-0410-aec6-3dcde31c8c00