Merge commit 'stew/knownchanges' into merge

* commit 'stew/knownchanges':
  trailing whitespace, update to 18 not 20
  update20 -> update 18
  removing known_changes now works, and inserting has a better chance of working
  update20 is closer to tested
  check for a DAK_CONFIG env variable when looking for dak.conf
  moved inserts of known_changes to Changes() class. add insert known_changes in p-u, remove known_changes in process_new.reject
  Start the known_changes table

Signed-off-by: Joerg Jaspert <joerg@debian.org>