Use timegm, or our already existing replacement instead of timezone, as

Use timegm, or our already existing replacement instead of timezone, as
some platforms (FreeBSD in this case) don't define timezone according to
posix.  This is what I wanted to do anyway.

Spotted by Andrzej Tobola <san@iem.pw.edu.pl>
(This used to be commit bc13e35db0b8b265f87553d4df1c7326710cb3fa)