Avoid some resource leaks

Avoid some resource leaks

* src/incremen.c (store_rename): Free temp_name, leaked before for
each renamed directory with --listed-incremental.
* src/transform.c (add_literal_segment): Tighten arguments by
const.
(parse_transform_expr): Free 'str', leaked storage for each
--transform option before.
* src/utf8.c (utf8_convert): Deallocate buffer for failed iconv()
call so callers don't have to.