relax checks in Variables.link_duals() for easier term evaluation
relax checks in Variables.link_duals() for easier term evaluation

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