[packagekit] Role Proposal RepairSystem and SimulateRepairSystem

[Sebastian Heinlein]

Hello,

It would be nice to have a set of a high level method to repair a broken
system. On the APT side we can recover from two situations:

* a failed/cancelled installation by running "dpkg -configure -a" to
complete the postinstallation scripts

* broken dependencies - APT provides a method to recover from this by
installing/removing packages

The first case is handled by the apt backend automatically on each
installation/removal/update: If the backend detects an incomplete
installation "dpkg --configure -a" will be called before running the
transaction.

If the backend runs into an error which could be repaired it should emit
the not yet existing error-system-broken error to indicate the client
that it should over the user to repair the system.

Since the RepairSystem role could end up installing packages it would
require an only_trusted argument.

What could happen to other package managers? What do you think about
this?

Cheers,

Sebastian