update create_evaluable() for Materials under Equations
update create_evaluable() for Materials under Equations

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