easier_terms: use vg.integrate() in de_grad, de_div terms
easier_terms: use vg.integrate() in de_grad, de_div terms

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