parse-options: fix leaks for users of OPT_FILENAME

The `OPT_FILENAME()` option will, if set, put an allocated string into
the user-provided variable. Consequently, that variable thus needs to be
free'd by the caller of `parse_options()`. Some callsites don't though
and thus leak memory. Fix those.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/helper/test-parse-options.c

@@ -207,6 +207,7 @@ int cmd__parse_options(int argc, const char **argv)
 	expect.strdup_strings = 1;
 	string_list_clear(&expect, 0);
 	string_list_clear(&list, 0);
+	free(file);
 
 	return ret;
 }