add TAIL_COPY_THRESHOLD to depth computed for closure bodies to avoid runstack overflow
add TAIL_COPY_THRESHOLD to depth computed for closure bodies to avoid runstack overflow

svn: r5505

mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket