virtualbox-guest update breaks gvfs smb mounts

[Mark Crutch]

On Linux Mint 17 Mate (Qiana) a recent update to the virtualbox-guest-* packages (4.3.34-dfsg-1+deb8u1ubuntu1.14.04.1) has broken gvfs functionality when using smb mounts.

Trying to access an SMB share using a bookmark in Caja causes a new window to open which appears to be un-themed (1990s style buttons and scrollbars). It's no longer possible to open files via the /var/run/user/1000/gvfs/ mount points in certain applications (e.g. Geany). Trying to double-click on a file that should be associated with Geany opens Pluma instead.

Reverting back to an older version of these packages, or removing them entirely, fixes the issue.