rerere: fix various trivial leaks

We leak various different string lists in the rerere code. Free those to
plug them.

Note that the `merge_rr` variable is intentionally being free'd with the
`free_util` parameter set to 1. The `util` field is used there to store
the IDs of every rerere item and thus needs to be freed, as well.

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

rerere.c

@@ -849,6 +849,8 @@ static int do_plain_rerere(struct repository *r,
 	if (update.nr)
 		update_paths(r, &update);
 
+	string_list_clear(&conflict, 0);
+	string_list_clear(&update, 0);
 	return write_rr(rr, fd);
 }
 
@@ -912,6 +914,7 @@ int repo_rerere(struct repository *r, int flags)
 		return 0;
 	status = do_plain_rerere(r, &merge_rr, fd);
 	free_rerere_dirs();
+	string_list_clear(&merge_rr, 1);
 	return status;
 }