nautilus freeze break request

[Alexander Larsson <alexl redhat com>]

There is an error in nautilus where you can't mount+unmount the same
share twice. You'll get an error on unmount the second time. The reason
for this is that we keep around a reference to the first GMount object
which goes stale, and then the second time we unmount we try to unmount
the first mount again.

Bug: http://bugzilla.gnome.org/show_bug.cgi?id=529295
Patch: http://bugzilla.gnome.org/attachment.cgi?id=130394&action=view