git p4: move conflict prompt into run, add [q]uit input

git p4: move conflict prompt into run, add [q]uit input

When applying a commit to the p4 workspace fails, a prompt
asks what to do next.  This belongs up in run() instead
of in applyCommit(), where run() can notice, for instance,
that the prompt is unnecessary because this is the last commit.

Offer two options about how to continue at conflict: [s]kip or
[q]uit.  Having an explicit "quit" option gives git p4 a chance
to clean up, show the applied-commit summary, and do tag export.

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