Simplifications for UUO links etc.

[JONL at MIT-MC (Jon L White)]

1) Hau about flushing the alternative for lap and fasload which
   permits the "snapping" of CALLs and JCALLs during loading etc.
   The only alternatives then would be PURE = NIL and PURE = non-NIL.
   With the new incrementally-extendible UUOLINKS area, and its smaller
   size, there seems to be little reason not to use it in all cases
   wherein some purification is desired.
2) According to GSB, the UUO clobberer should bypass the clobbering
   on any binary-program page which is considered pure.  There is come
   code in the UUO handler which tries to decide whether or not to
   clobber - perhaps we could merely extend it to inspect the GCST for
   the page in question, and it it is alleged to be pure, then cancel.