Use constant E_RECOVERABLE_ERROR, E_DEPRECATED and E_USER_DEPRECATED instead of int code.

The constant `E_RECOVERABLE_ERROR`, `E_DEPRECATED` and `E_USER_DEPRECATED` are part of PHP since 5.2.0 (recoverable error) respectively 5.3.0 and should be used instead of the int code.
See http://php.net/manual/de/errorfunc.constants.php