fix insert_sub_reqs() for arbitrary order of leaf requirements
fix insert_sub_reqs() for arbitrary order of leaf requirements

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