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>

builtin/sparse-checkout.c

@@ -1011,6 +1011,7 @@ static int sparse_checkout_check_rules(int argc, const char **argv, const char *
 
 	ret = check_rules(&pl, check_rules_opts.null_termination);
 	clear_pattern_list(&pl);
+	free(check_rules_opts.rules_file);
 	return ret;
 }