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

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

* 'master' of ssh://ftp-master.debian.org/srv/ftp.debian.org/git/dak:
  Fix very bad logic error
  Fix Release file hardlink handling
  Fix typo
  Fix database permissions
  Avoid using an SQL keyword as a column name
  Apply update 56
  Update pickle file for DB tests.
  Add PackagesFileWriter and SourcesFileWriter.
  Implement SourceContentsFileWriter.
  various bugfixes
  Allow per-suite signing keys
  Add the *FileWriter helper classes.