Got basic kernel compression working. Lots left to do:
- figure out how we're going to pass the compressed core length to
  savecore, probably write a header before the gzip header on the media.
- figure out why the hell things go crazy if I allocate scratch space
  for zlib using malloc in set_dumper(). When I use the BSS everything
  is fine as far as I can see.
- refactor the dumper API. At the moment I'm kind of fighting it. Some
  background is needed first though, e.g. why do we write kernel core
  dumps to the end of media?