t1410: make hash size independent

t1410: make hash size independent

Instead of parsing object IDs using fixed-length shell patterns, use cut
to extract the first two characters of an object ID in addition to the
test helper for object paths.  Update another test to look up an
appropriate object ID fragment from the all-zeros object ID instead of
hardcoding the value.

Although the test for parsing reflogs at BUFSIZ boundaries passes, mark
it with the SHA1 prerequisite, as it doesn't currently usefully test
anything when using a hash longer than 20 bytes.

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