gvfs freeze break - multiple icons for audio cd

[Alexander Larsson <alexl redhat com>]

In this release we introduced the concept of "shadowed" mounts. A mount
is shadowed when some other UI element more or less "takes over" it
UI-wise. For instance, When the hal volume monitor detects a cd drive
with an audio cd in it it generates a mount object that shadows the
"real" gvfs audio cd mount, so that the mount appears as being in the cd
drive volume (otherwise hard since these are different types of mounts).

Most code is updated to not show shadowed mounts, however it seems we
forgot to handle this in computer://.

Bug: http://bugzilla.gnome.org/show_bug.cgi?id=572521
Patch: http://bugzilla.gnome.org/attachment.cgi?id=130448&action=view

Can i commit this?