update get_condition_value() to provide more helpful messages on errors
update get_condition_value() to provide more helpful messages on errors

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