macos:  Short-circuit CopyRgn_patch() on identity
macos:  Get dest rgn size from rgnSize, not Handle
macos:  Add empty_rect() predicate
macos:  Call empty_region() from EmptyRgn_patch()
quickdraw:  Return data end from set_region_bbox()
macos:  Add _XOrRgn trap
region-math.mac:  Add _XOrRgn tests