fix ProblemDefinition.solve() to preserve evaluate caches
fix ProblemDefinition.solve() to preserve evaluate caches

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