[packagekit] no-more-c-structures

[Richard Hughes]

I've just merged in the no-more-c-structures branch to
packagekit-glib2 in git master. It's a pretty big diffstat, but it's
basically just changing the PkItemFoo C structures into proper Glib
GObjects. This allows us to extend them in the future without breaking
ABI or API and also allows cool things like introspection and getting
bindings for free.

I've converted all the in-tree users, but please can you test compile
your backend in the next three weeks before the next release. If you
have any problems, yell at me and I'll fix things up for you.

packagekit-glib has not been changed for obvious reasons, so the
existing users of packagekit-glib (not glib2) do not have to be
recompiled. Thanks.

Richard.