t9300: use test_cmp_bin instead of test_cmp to compare binary files

test_cmp is intended to produce diff output for human consumption. The
input in one instance in t9300-fast-import.sh are binary files, however.
Use test_cmp_bin to compare the files.

This was noticed because on Windows we have a special implementation of
test_cmp in pure bash code (to ignore differences due to intermittent CR
in actual output), and bash runs into an infinite loop due to the binary
nature of the input.

Signed-off-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Merge pull request #2 from t-b/tb_more_use_of_test_cmp_bin

t9300: use test_cmp_bin instead of test_cmp to compare binary files