Misc range temporary fixes.

Misc range temporary fixes.

This fixes a couples places that were using int_range_max, but needed
a generic temporary.  Found while merging the frange work.

Also, copying between range temporaries is actually useful :).

Tested on x86-64 Linux.

gcc/ChangeLog:

	* gimple-range-cache.cc (ranger_cache::range_from_dom): Use
	Value_Range.
	* gimple-range.cc (gimple_ranger::register_inferred_ranges): Same.
	* value-range.h (Value_Range::Value_Range): Implement copy
	constructor for Value_Range.