update IGDomain.__init__() to initialize cell_offsets attribute
update IGDomain.__init__() to initialize cell_offsets attribute

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