update multilinear terms: make de_convect evaluable
update multilinear terms: make de_convect evaluable

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