[PATCH] Trapping exit in tests, using return for errors: further fixes.

[PATCH] Trapping exit in tests, using return for errors: further fixes.

"return" from a test would leave the exit trap set, which could cause a
spurious error message if it's the last test in the script or
--immediate is used.

The easiest solution would be to have a global trap that is set when
test-lib.sh is sourced and unset either by test_done(), error() or by
test_failure_() with --immediate.

Signed-off-by: Pavel Roskin <proski@gnu.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>