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

def attribute(self, project, attribute):
        """Returns the value of the specified attribute in the
        specified jamfile module."""
        assert isinstance(project, basestring)
        assert isinstance(attribute, basestring)
        try:
            return self.module2attributes[project].get(attribute)
        except:
            raise BaseException("No attribute '%s' for project %s" % (attribute, project))