fix schroedinger.py for meshes with several element groups
fix schroedinger.py for meshes with several element groups

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