apply: Recognize epoch timestamps with : in the timezone

Some patches have a timezone formatted like ‘-08:00’ instead of
‘-0800’ (e.g. http://lwn.net/Articles/131729/

), so git apply would
fail to recognize the epoch timestamp of deleted files and would
create empty files instead.  Teach it to support both formats, and add
a test case.

Signed-off-by: Anders Kaseorg <andersk@mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>