added msg_if_none kwarg to get_default_attr()
added msg_if_none kwarg to get_default_attr()

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