[packagekit] API BREAK: UpdateDetail

[Richard Hughes]

I've broken internal and external API in git master to add four extra
fields to UpdateDetail. The fields are changelog, status, issued and
updated. They'll let enterprise tools filter the updates in more
specific ways, and provide more data to the user about the update.

I think I've converted all backends, although it's probably best to
check that everything works okay.

I'll add the extra detail into gpk-update-viewer this afternoon.

This is the last API break before 0.3.0 -- so you can expect a new
branch to be forked soon.

Richard.