... so that this option can be disabled on systems that don't support it.
This also allows to use another compression program, such as pbzip2 on SMP
machines (closes Roundup bug #2405).

... for rdiff.helper, dup.helper, example.dup and example.rdiff.

... instead of previous /var/backups/duplicity.

This is the only way to securely transmit the FTP password from backupninja
to duplicity.

I'd love to use "dpkg --compare-versions" but we don't want backupninja to be
Debian-specific. Any similar tool?

Signed-off-by: intrigeri <intrigeri@boum.org>

This is necessary to get rid of unnecessary old cache files when cleaning up,
when using duplicity >=0.6.01 that depends on local caching.

Closes: #572721

to improve the ninjahelper interface as requested by alster in redmine

something to the changelog all for 98e62c95

Thanks to maniacmartin <martin@maniacmartin.com> for the patch on which this one
is based.
This closes Redmine bug #1209.