fix and simplify LCBCOperator.treat_pbcs()
fix and simplify LCBCOperator.treat_pbcs()

- LCBCs combined with EPBCs in common nodes work correctly (second try)
  - in particular for non-penetration conditions with general normals

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