upgraded to VirtualBox 4.2.12
Merge commit 'ad295968443a689c7c769b77f6497746ce71e083'

Merging upstream 4.2.4 -> 4.2.12

The conflict in dirops.c was straightforward: upstream removed some code near
one of our patches. Resolved by removing the code in ours too.

The conflict in VBoxGuestR0LibSharedFolders was because upstream added a
function that was very similar to one we added, so the diffs got interleaved.
Resolved by including both functions.

Conflicts:
	virtualbox/src/VBox/Additions/common/VBoxGuestLib/VBoxGuestR0LibSharedFolders.c
	virtualbox/src/VBox/Additions/common/VBoxGuestLib/VBoxGuestR0LibSharedFolders.h
	virtualbox/src/VBox/Additions/linux/sharedfolders/dirops.c