fix FieldVariable.__init__() to initialize .history attribute
fix FieldVariable.__init__() to initialize .history attribute

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