Merge branch 'master' of ssh://franck.debian.org/srv/ftp.debian.org/git/dak

Merge branch 'master' of ssh://franck.debian.org/srv/ftp.debian.org/git/dak

* 'master' of ssh://franck.debian.org/srv/ftp.debian.org/git/dak:
  Extend test_poolfiles().
  Add a test for PoolFile and Location.
  Mark Location.archive_type as obsolete.
  Carefully add a backref from PoolFile to Location.
  Add an incomplete test for Maintainer.
  Make relation Maintainer - DBSource bidirectional.
  TimestampTestCase: replace sql string by func.now.
  DBSource: drop property srcassociations.