Get all parents/relationships on this GOTerm.

def _getobjs_higher(self, goobj):
        """Get all parents/relationships on this GOTerm."""
        goobjs_higher = set(goobj.parents)
        for reltyp, relgoobjs in goobj.relationship.items():
            if reltyp in self.relationships:
                goobjs_higher.update(relgoobjs)
        return goobjs_higher