1.0.17.7: smaller and faster raw slot initialization on x86oids

1.0.17.7: smaller and faster raw slot initialization on x86oids

 * Since %MAKE-STRUCTURE-INSTANCE knows exactly how long the instance
   will be, RAW-INSTANCE-INIT/* VOPs don't need to fetch the length at
   all, but can receive it as a direct argument.

 * Use (* INDEX N-WORD-BYTES) in MAKE-EA-FOR-RAW-SLOT instead of
   (FIXNUMIZE INDEX) -- same result, but the intention becomes clear.