Make the allow_implicit config check less strict.

I'm writing OAuth2 Server integration for Drupal, based on this library.
(Currently at http://drupal.org/sandbox/bojanz/1928198).)

Drupal stores the allow_implicit setting as an integer, which means that the library gets 0 or 1 instead of FALSE or TRUE.
Since the library uses an identical check (===) for the setting, it fails to work correctly.

I see no harm in switching to a less strict check.