mingw: try to work around issues with the test cleanup

It seems that every once in a while in the Git for Windows SDK, there
are some transient file locking issues preventing the test clean up to
delete the trash directory. Let's be gentle and try again five seconds
later, and only error out if it still fails the second time.

This change helps Windows, and does not hurt any other platform
(normally, it is highly unlikely that said deletion fails, and if it
does, normally it will fail again even 5 seconds later).

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

Author: dscho

t/test-lib.sh

@@ -971,7 +971,11 @@ test_done () {
 			error "Tests passed but trash directory already removed before test cleanup; aborting"
 
 			cd "$TRASH_DIRECTORY/.." &&
-			rm -fr "$TRASH_DIRECTORY" ||
+			rm -fr "$TRASH_DIRECTORY" || {
+				# try again in a bit
+				sleep 5;
+				rm -fr "$TRASH_DIRECTORY"
+			} ||
 			error "Tests passed but test cleanup failed; aborting"
 		fi
 		test_at_end_hook_