git p4: notice Jobs lines in git commit messages

git p4: notice Jobs lines in git commit messages

P4 has a feature called "jobs" that allows linking changes
to a bug tracking system or other tasks.  When submitting
code, a job name can be specified to mark that this change
is associated with a particular job.

Teach git-p4 to find an optional "Jobs:" line in git commit
messages and use them to make a Jobs section in the p4
change specifitation.

Signed-off-by: Pete Wyckoff <pw@padd.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>