Patches from git passed into p4 end up with the committer being identified
as the person who ran git-p4.

With "submit --preserve-user", git-p4 modifies the p4 changelist (after it
has been submitted), setting the p4 author field.

The submitter is required to have sufficient p4 permissions or git-p4
refuses to proceed. If the git author is not known to p4, the submit will
be abandoned unless git-p4.allowMissingP4Users is true.
Signed-off-by: NLuke Diamand <luke@diamand.org>
Acked-by: NPete Wyckoff <pw@padd.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>