1.0.5.53: cleanup LOAD-TYPE macros

1.0.5.53: cleanup LOAD-TYPE macros

	* when the LOAD-TYPE macros in the various backends hardcoded '3',
	  they really meant (1- N-WORD-BYTES)--a little reflection on
	  widetags, lowtags, and endian orderings should make this clear
	  (we don't have a 64-bit big-endian port to drive it home, though);
	* catch the spread of magic constants in code/array.lisp.