mingw: demonstrate that all file handles are inherited by child processes

When spawning child processes, we really should be careful which file
handles we let them inherit.

This is doubly important on Windows, where we cannot rename, delete, or
modify files if there is still a file handle open.

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

t/t0061-run-command.sh

@@ -12,6 +12,10 @@ cat >hello-script <<-EOF
 	cat hello-script
 EOF
 
+test_expect_failure MINGW 'subprocess inherits only std handles' '
+	test-tool run-command inherited-handle
+'
+
 test_expect_success 'start_command reports ENOENT (slash)' '
 	test-tool run-command start-command-ENOENT ./does-not-exist 2>err &&
 	test_i18ngrep "\./does-not-exist" err