test: git-stash conflict sets up rerere

test: git-stash conflict sets up rerere

Add a test to make sure that a conflicted "stash apply" invokes
rerere to record the conflicts and resolve the the files it can
(the current code doesn't, so the test is marked as failing).

Without correct state recorded for rerere, mergetool may be
confused, causing it to think no files have conflicts even though
they do.  This condition is not verified by this test since a
subsequent commit will change the behavior to enable rerere for
stash conflicts.

Also, the next test expected us to finish up with a reset, which is
impossible to do if we fail (as we must) and it's an unreasonable
expectation anyway.  Begin the next test with a reset of its own
instead.

Signed-off-by: Phil Hord <hordp@cisco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>