Add a dom based ranger for fast VRP.

Add a dom based ranger for fast VRP.

Provide a dominator based implementation of a range query.

	* gimple-range.cc (dom_ranger::dom_ranger): New.
	(dom_ranger::~dom_ranger): New.
	(dom_ranger::range_of_expr): New.
	(dom_ranger::edge_range): New.
	(dom_ranger::range_on_edge): New.
	(dom_ranger::range_in_bb): New.
	(dom_ranger::range_of_stmt): New.
	(dom_ranger::maybe_push_edge): New.
	(dom_ranger::pre_bb): New.
	(dom_ranger::post_bb): New.
	* gimple-range.h (class dom_ranger): New.