This release should be now stable enough for release

/reviewed-on !391

This reverts commit 9b3dfa01

  This version contains optimisation for restore (and a bit for backup), specially in case of large sets of unmodified files.

Replace dropbear by openssh.
Use same rdiff-backup than provided by PBS.
Allow to directly use an IPV6 address with a custom port.

It prevents data loss while upgrading partition.

This automatically handle lxml installation.

Request the service with the software type pullrdiffbackup.

Real backup are added by request a slave with required parameters:
  hostname="example.org" (just to make think readable for human)
  connection="user@0.0.0.0" (ssh connection string)
  include="/src /home" (space separated directory path to backup)
  frequency="0 0 * * *" (crontab like periodicity string)

Optional parameters are:
  exclude="/home/userA /home/userB" (space separated directory path to not backup)
  sudo="True" (if the server to backup contains a local backupagent_rdiff-backup script which is callable with sudo)