duplicity 0.6.17 uses paramiko backend.
Thus, it does not support limiting bandwidth anymore.
Let's use trickle to support bandwidth shaping anyway.

Recent versions of automake prevent us from installing lib/* into
lib/backupninja/. Where else are be supposed to install such files anyway?

Locking its tables require privileges the 'debian-sys-maint'@'localhost' user is
generally not granted.

Thanks to Yuval Kogman <nothingmuch@woobling.org> for the patch.

I.e. document tmpdir.

Thanks to Olivier Berger <oberger@ouvaton.org> for the patch.
(Closes Redmine bug #3443)
(Closes: #641120)

when=XXX did work already. This patch allow to write this with spaces around the
equal sign - as in every other backup.d/ file.

cut is in /usr/bin actually.