improved toString method of PredicateStats
Fixed handling of negative predicate in frontier size estimation method.
Fixed handling of negative predicate id in frontier size estimation method.
Increased number of counting query test runs.
added two optimizer tests
i) Fixed wrong default values for statistics maps and ii) decreased the timeout for counting query and will crash if it times out
Removed println.
Added assert around === statements to ensure tests fail when there's no match.
Improved toString method of PredicateSelectivity.
Added query elimination when the stats are reliable and when a query has no results according to the stats.
Added test case that reproduces inefficient optimizer result.