Currently it is not possible to skip the submission of a change to Perforce
when running git-p4 submit. This patch compares the modification time before
and after the submit editor invokation and offers a prompt for skipping if
the submit template file was not saved.
Signed-off-by: Simon Hausmann <simon@lst.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>