[packagekit] Making UpdatePackage() into UpdatePackages()

[Richard Hughes]

I've just merged a patch to turn UpdatePackage() into UpdatePackages() -
this lets us do some cool things like only update security updates and
also select the updates individually in pk-update-viewer.

I think all the backends should still compile, and should work to some
effect. Where it's not obvious what to do do I've just treated
UpdatePackages() like we've only got one argument and ignored the rest -
how you fix this depends on how clever your backend is.

The spawned backends just get more command line arguments. Everything
else gets a char** to play with.

So please test test test and hopefully we can get a release out fairly
soon (this weekend?). Thanks guys.

Richard.