shorten FieldVariable.set_from_function()
shorten FieldVariable.set_from_function()

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