Merge commit 'mhy/checksums'

* commit 'mhy/checksums':
  expand check_archive.py to cope with extra checksums
  add changelog to keep Ganneff happy
  add sha1sum and sha256sum columns
  fix typos
  make process accepted not die with old .dak files
  an attempt to move the functionaliity into a module
  let's store the known_hashes information centrally
  first attempt at bodging in support for sha1sum and sha256sum