Returns the value of the specified attribute in the
        specified jamfile module.

def attributeDefault(self, project, attribute, default):
        """Returns the value of the specified attribute in the
        specified jamfile module."""
        assert isinstance(project, basestring)
        assert isinstance(attribute, basestring)
        assert isinstance(default, basestring) or default is None
        return self.module2attributes[project].getDefault(attribute, default)