revset: changed sort method to use native sort implementation of smartsets When sort is done by revision or reversed revision number it can just call sort on the set and doesn't have to iterate it all over again.

revset: fixed sorting issue with spanset When a spanset was being sorted it didn't take into account it's current state (ascending or descending) and it reversed itself everytime the reverse parameter was True. This is not yet used but it will be as soon as the sort revset is changed to directly use the structures sort method.

tests: added tests to test sort revset This tests are intended to test sort in many different cases where it could fail when using the new structures

revset: added __nonzero__ method to spanset class Implemented it in a lazy way, just look for the first non-filtered revision and return True if there's any revision at all.