Add SB-SYS:SAP-REF-LISPOBJ.

Add SB-SYS:SAP-REF-LISPOBJ.

  * This is for those cases where you know that you are trying to
read valid boxed data, the address of the data you want to read
is in some sense "stable" (meaning, won't be moved by the GC),
and you don't want to deal with the requirements for calling
SB-KERNEL:MAKE-LISP-OBJ.

  * Implemented across the board, but only tested on PPC.  What
could possibly go wrong?