add alternative mechanism support

Signed-off-by: Mattias Andrée <maandree@operamail.com>
derp

Signed-off-by: Mattias Andrée <maandree@operamail.com>
autocleanup of links in /etc/alternatives + print information about changes in /etc/alternatives

Signed-off-by: Mattias Andrée <maandree@operamail.com>