Teach "git stripspace" the --strip-comments option

With --strip-comments (or short -s), git stripspace now removes lines
beginning with a '#', too.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t0030-stripspace.sh

@@ -392,4 +392,9 @@ test_expect_success \
     git diff expect actual
 '
 
+test_expect_success 'strip comments, too' '
+	test ! -z "$(echo "# comment" | git stripspace)" &&
+	test -z "$(echo "# comment" | git stripspace -s)"
+'
+
 test_done