hom: support recursive requirements in HomogenizationEngine
hom: support recursive requirements in HomogenizationEngine

- added insert_sub_reqs(), HomogenizationEngine.compute_requirements()

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