building without volume_id

[Frederic Peters]

Hello,

I am monitoring GNOME builds on http://jhbuild.bxlug.be and HAL new
dependency on libvolume_id (or libvolume_id move to udev) is causing
troubles.

I had two options :

 - adding a new volume_id module, using git to grab the latest version
   from udev.  Unfortunately I can't get git to only clone a sub
   directory (extras/volume_id/lib) and this makes integration within
   jhbuild difficult.
 
 - adding a new configure check to HAL, specifically checking for
   volume_id, and disabling volume_id calls in probe-storage/volume if
   it was not found.  This is the path taken in the attached patch.

Would this be considered for inclusion ?


Thanks,

        Frederic