tests: notice valgrind error in test_must_fail
tests: notice valgrind error in test_must_fail

We tell valgrind to return 126 if it notices that something is wrong,
but we did not actually handle this in test_must_fail, leading to
false negatives.  Catch and report it.

Signed-off-by: Thomas Rast <18f23ef7096473d837b7404952f13710423b8b63@inf.ethz.ch>
Acked-by: Johannes Schindelin <b4cf3b77c95aaa57254d96e276bf14cfc9472402@gmx.de>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git