producing // paths for thumbnails

first you do:
// A CLI-server hack
"cli-server" === php_sapi_name() && !defined('FILE_CACHE_DIRECTORY')
    && define('FILE_CACHE_DIRECTORY', BOLT_CACHE_DIR . '/thumbs/');
SO "$this->cachefile = $this->cacheDirectory . '/' . FILE_CACHE_PREFIX"... will be like /thumbs/ . /timthumb/longnamewithsalt.tmp

get it?

Also should be added to support docs, "check for GD being installed for thumbnails to work"