LLP64: change UNSIGNED-LONG to UNSIGNED

LLP64: change UNSIGNED-LONG to UNSIGNED

Adjust references to alien types within Lisp code for LLP64 platforms,
replacing UNSIGNED-LONG with UNSIGNED.

UNSIGNED-LONG is currently used when pointer-size values are desirable,
but does not have that meaning on LLP64 platforms.

Note: UNSIGNED does not in general refer to C's `unsigned'; rather it
means (UNSIGNED N-WORD-BITS).  UNSIGNED-LONG actually means `unsigned
long'.  The implication is that

  32 <= sizeof(UNSIGNED-LONG) <= sizeof(UNSIGNED) <= 64

and not, as one might have expected, the other way around.  Existing
platforms were assuming these two types to be the same.

Thanks to Anton Kovalenko.