This switches git-commit-tree to using curl_getdate() for the
AUTHOR_DATE, and thus fixes the problem with "mktime()" parsing dates in
the local timezone.  It also ends up being more permissive about the
format of the date. 
Signed-off-by: NTony Luck <tony.luck@intel.com>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>