Update FileStorage.php

Strict compliance with new CakePhp 2.4.1, see
http://bakery.cakephp.org/articles/markstory/2013/09/15/cakephp_2_4_1_released

Method signatures of Behavior callbacks was corrected. If you are using PHP5.4 you may have to update the method signatures of your behaviors to resolve any E_STRICT errors.