Correct the boolean handling

Casting to (bool) is equivalent to using boolval()
see
http://php.net/manual/en/function.boolval.php
http://php.net/manual/en/language.types.boolean.php

it closes #441

Signed-off-by: Etienne CHAMPETIER <etienne.champetier@fiducial.net>
Merge pull request #442 from echampet/bool

Correct the boolean handling