inline declaration for FLET and LABELS

[Jonathan A Rees <JAR@MC.LCS.MIT.EDU>]

I've implemented it a couple times and never had any trouble, but then
I've never tried to write a compiler which tried to implement
optimizations via macro expansion.  It's best in lexical languages
either to uniquely rename user variables like RABBIT does, or to make
"virtual closures" to make sure that lambda-expressions know what
lexical environment they came from (I've never tried that although I
think it would work).  The LETREC case seems harder to me since you have
to deal with mutual recursion.