t5400-send-pack relies on a working cpio

Since cygwin does not install cpio by default, t5400 results in a very
cryptic failure. So, test for cpio explicitely.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <junkio@cox.net>

t/t5400-send-pack.sh

@@ -8,6 +8,9 @@ test_description='See why rewinding head breaks send-pack
 '
 . ./test-lib.sh
 
+touch cpio-test
+test_expect_success 'working cpio' 'echo cpio-test | cpio -o > /dev/null'
+
 cnt='1'
 test_expect_success setup '
 	tree=$(git-write-tree) &&