Luke Diamand authored Aug 27, 2015 and Junio C Hamano committed Aug 28, 2015

With --detect-labels enabled, git-p4 will try to create tags
using git fast-import by writing a "tag" clause to the
fast-import stream.

If the commit that the tag references has not yet actually
been processed by fast-import, then the tag can't be created
and git-p4 fails to import the P4 label.

Teach git-p4 to use fast-import "marks" when creating tags
which reference commits created during the current run of the
program.

Commits created before the current run are still referenced
in the old way using a normal git commit.

Signed-off-by: Luke Diamand <luke@diamand.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>