Add a return value to intersect and speed it up.

Add a return value to intersect and speed it up.

Return true if the intersection of ranges changed the original value.
Speed up the case when there is no change by calling an efficient
contains routine.

	* value-range.cc (irange::legacy_verbose_intersect): Add return value.
	(irange::irange_contains_p): New.
	(irange::irange_intersect): Add return value.
	* value-range.h (class irange): Adjust prototypes.