revisions API users: add "goto cleanup" for release_revisions()

Add a release_revisions() to various users of "struct rev_info" which
requires a minor refactoring to a "goto cleanup" pattern to use that
function.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/stash.c

@@ -917,6 +917,7 @@ static int show_stash(int argc, const char **argv, const char *prefix)
 cleanup:
 	strvec_clear(&stash_args);
 	free_stash_info(&info);
+	release_revisions(&rev);
 	if (do_usage)
 		usage_with_options(git_stash_show_usage, options);
 	return ret;