[packagekit] ServicePack: depending on gio

[Richard Hughes]

For the ServicePack functionality we need to do some pretty fancy things
with volumes, and I want to use gio for that as quite frankly, the API
rocks.

Now, I appreciate some of you guys might not want the additional dep on
gio as it's quite new, and not in any released distro versions.

I've therefore made this detectable at build time in the configure
script - if you have no GIO then you don't get the ServicePack
functionality and you get a dummy PkVolumeMonitor GObject build that
does nothing.

I won't push this local branch into git master until after I've released
0.1.10 as else I'm breaking my own rules :-)

Following this email will be specific thread for discussion. So no code
yet -- but I'm working on it.

Richard.