test-sha1: add a binary output mode

test-sha1: add a binary output mode

The test-sha1 helper program will run our internal sha1
routines over its input and output the 40-byte hex sha1.
Sometimes, however, it is useful to have the binary 20-byte
sha1 (and it's a pain to convert back in the shell). Let's
add a "-b" option to output the binary version.

Signed-off-by: Jeff King <redacted>
Acked-by: Nicolas Pitre <redacted>
Signed-off-by: Junio C Hamano <redacted>