git-p4: fix submit regression with clientSpec and subdir clone

git-p4: fix submit regression with clientSpec and subdir clone

When the --use-client-spec is given to clone, and the clone
path is a subset of the full tree as specified in the client,
future submits will go to the wrong place.

Factor out getClientSpec() so both clone/sync and submit can
use it.  Introduce getClientRoot() that is needed for the client
spec case, and use it instead of p4Where().

Test the five possible submit behaviors (add, modify, rename,
copy, delete).

Reported-by: Laurent Charrière <lcharriere@promptu.com>
Signed-off-by: Pete Wyckoff <pw@padd.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>