LET macro & fsubr

[RLB at MIT-MC (Richard L. Bryan)]

Before it's too late, why not generalize it to allow atomic symbols in the
bind list. If these occur, bind to NIL in the interpreter, and in compiled
code, to the appropriate zero.
Thus, at macro level,
 (let ((a 'a) b c) . body) becomes
 ((lambda (a b c) . body) 'a nil nil)
This is only a little harder than mapcar'ing 'CAR or 'CADR over the lists,
and the DO equivalent required might accomplish additional error checking.