fixed bugs in comparison of tightness of range bounds, and made it so that invalid ranges insert NoResultNode in the plan.
added method to check if a range info contains a unique value, and cleaned up FilterToEnumCollFinder.
fixing comparison of bounds.
Merge branch 'aql2' of ssh://github.com/triAGENS/ArangoDB into aql2

Conflicts:
	arangod/Aql/OptimizerRules.cpp