[packagekit] Updated backends now crashing

[Anders F Björklund]

> "This method simulates a package instalation emitting packages required to be installed, removed, updated, reinstalled, downgraded, obsoleted or untrusted. The latter is used to present the user untrusted packages that are about to be installed."
> 
> It doesn't really mention anything about ordering or dependencies ?

As discussed, it doesn't need to be ordered but should include depends.

> I'm not entirely sure about the difference between updated / obsoleted,
> but I guess the new pkg is "updated", and the old pkg is "obsoleted" ?
> All the changeset has is a list of pkgs to install and pkgs to remove.

This needs to be determined based on the changeset install/removes...

If the name is the same, it's an "update" or "downgrade", otherwise
it's an "obsolete". If both name/version are the same, it's a "reinstall" 

Untrusted will require more work, as that info might be in the channel*.

* e.g. in apt channels the packages aren't signed separately, but the
checksums of all packages are signed together. "Package" needs to know.

--anders