bitvectors verses bignums

[George J. Carrette <GJC at MIT-MC>]

MOON's original note pointed out that no side-effecting operations
had been given at the time for bitvectors. This was a fairly
silly oversight, now fixed.

In any case there is a subtle difference between them, the meaning
of the LENGTH. You can have a bitvector 100 bits long, with all bits zero,
but you cannot have a number 100 bits long which is 0.

-GJC

p.s. On the lexical-scoping issue: I am working on a note summarizing 
     USER-EXPERIENCE and comments collected over the last year that the 
     "hail-mary" versions of NIL have been in use, since lexical-scoping
     caused the most people the most problems.