Output common validator types based on usage.

def _output_validators(self):
        """Output common validator types based on usage."""
        if self._walk_for_type('Boolean'):
            print("from .validators import boolean")
        if self._walk_for_type('Integer'):
            print("from .validators import integer")
        vlist = self.override.get_validator_list()
        for override in vlist:
            if override.startswith('common/'):
                override = override.lstrip('common/')
                filename = "validators"
            else:
                filename = "%s_validators" % self.filename
            print("from .%s import %s" % (filename, override))