git-p4: add tests demonstrating spec overlay ambiguities

git-p4: add tests demonstrating spec overlay ambiguities

Introduce new tests that look more closely at overlay situations
when there are conflicting files.  Five of these are broken.
Document the brokenness.

This is a fundamental problem with how git-p4 only "borrows" a
client spec.  At some sync operation, a new change can contain
a file which is already in the repo or explicitly deleted through
another mapping.  To sort this out would involve listing all the
files in the client spec to find one with a higher priority.
While this is not too hard for the initial import, subsequent
sync operations would be very costly.

Signed-off-by: Pete Wyckoff <pw@padd.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>