easier_terms: update Variable.__call__() history behaviour for step 0
easier_terms: update Variable.__call__() history behaviour for step 0

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