More Ranger cache tweaks

More Ranger cache tweaks

This patch splits the individual value propagation out from fill_block_cache,
and calls it from set_global_value when the global value is updated.
This ensures the "current" global value is reflected in the on-entry cache.

	* gimple-range-cache.cc (ssa_global_cache::get_global_range): Return
	true if there was a previous range set.
	(ranger_cache::ranger_cache): Take a gimple_ranger parameter.
	(ranger_cache::set_global_range): Propagate the value if updating.
	(ranger_cache::propagate_cache): Renamed from iterative_cache_update.
	(ranger_cache::propagate_updated_value): New.  Split from:
	(ranger_cache::fill_block_cache): Split out value propagator.
	* gimple-range-cache.h (ssa_global_cache): Update prototypes.
	(ranger_cache): Update prototypes.