fix LCBCOperator.treat_pbcs(), update LCBCOperators.append()
fix LCBCOperator.treat_pbcs(), update LCBCOperators.append()

- LCBCs combined with EPBCs in common nodes work correctly now

RexFuzzle/sfepy,BubuLK/sfepy,vlukes/sfepy,BubuLK/sfepy,sfepy/sfepy,lokik/sfepy,lokik/sfepy,lokik/sfepy,rc/sfepy,RexFuzzle/sfepy,sfepy/sfepy,RexFuzzle/sfepy,rc/sfepy,vlukes/sfepy,sfepy/sfepy,rc/sfepy,vlukes/sfepy,lokik/sfepy,RexFuzzle/sfepy,BubuLK/sfepy