Cache source files inside ezini cache, so that we can reuse this list on read for checkng modified time instead of having to find all possible input files again. Furthermore, this removes the need for using file_exists on all calls to $ini->prepend.. as we don't care if folder exists or not, only that it might exist.

PHP does not cache files / folders that does not exist, so by only doing file stats on files we know should exists, we'll get a noticeable speed boost.