Merge branch 'virtualbox' of git://github.com/Calrama/nixpkgs

Update VirtualBox (and implicitly VirtualBox Guest Additions) to 4.3.6
and Oracle VM VirtualBox Extension Pack to 91406

Conflicts due to minor upgrade in the mean time

Conflicts:
	nixos/modules/virtualisation/virtualbox-guest.nix
	pkgs/applications/virtualization/virtualbox/default.nix
	pkgs/applications/virtualization/virtualbox/guest-additions/default.nix