Change commit_msg_is() in t/t7500-commit.sh to use test_cmp instead of
the shell's test function. Now if a test fails we'll get test_cmp
output showing us what failed.
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>