Checkpointing on moving runtime to whalesong (broken HEAD)

- Compiles with an error under WS:

match: no matching clause for '#(warning "whalesong: WARNING: Primitive Kernel Value continuation-mark-set-first has not been implemented\n" #f whalesong)
  context...:
   /usr/lib/racket/collects/racket/match/runtime.rkt:21:0: match:error
   /home/joe/src/whalesong/whalesong-helpers.rkt:85:20: loop

- Produces several failures (9 rather than 2) running main.arr, and hangs when
  printing one of the exceptions.  I assume my set implementation is probably
  broken.