t0027: make hash size independent

t0027: make hash size independent

Several parts of this test generate files that have specific hard-coded
object IDs in them.  We don't really care about what the object ID in
question is, so we turn them all to zeros.

However, because some of these values are fixed and some are generated,
they can be of different lengths, which causes problems when running
with SHA-256.  Furthermore, some assertions in this test use only fixed
object IDs and some use both fixed and generated ones, so converting
only the expected results fixes some tests while breaking others.
Convert both actual and expected object IDs to the all-zeros object ID
of the appropriate length to ensure that the test passes when using
SHA-256.

The astute observer will notice that both tr and sed are used here.
Converting the tr call to a sed y/// command looks logical at first, but
it isn't possible because POSIX doesn't allow escapes in y/// commands
other than "\\" and "\n".

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>