Except Operator for Gremlin.

Proposing an Except (alias Difference) operator for Gremlin query language.

Usage:
HasNot pattern - get all nodes that don't have a 'status' predicate to object 'cool'.
g.V().Except(g.V().Has('status', 'cool')).All()

A.Except(B) - where A and B are complete iterators (not morphisms). The result will be the elements of A which do not appear in B (hence the "difference" alias for it).