VBOX: Fix crash if DVD-ROM media had been ejected by some external event.  Technically this shouldn't be happening, but something funky is going on with VirtualBox and we need to handle things that may cause a crash when cleaning up the VM.

VBOX: Make the service install scenario work again.

VBOX: When checking for the existence of a VM registered to a given slot directory, also check for the ISO Contextualization image and cache disk image.  If any type of media is registered to a given slot directory, close it regardless if it is attached to a VM or not.

VBOX: When deregistering a VM, organize the medium list by most recent child first and then release as needed.

VBOX: Introduce the notion of Virtualbox COM namespaces. We currently support VirtualBox 4.2 and VirtualBox 4.3.

VBOX: Do not attempt to restore the current snapshot if the VM hasn't been running long enough to generate one.

VBOX: If something fails during create_vm(), we must release the write lock before deregister_vm() is called. Handle machine and session cleanup at the end if the routine.

VBOX: Move common code to VBOX_BASE class, VBOX_VM derives from it by extending virtual functions calling Vboxmanage or Native API functions.  Use ATL on Windows to wrap COM Objects and data types.

VBOX: Begin refactoring for supporting the native VirtualBox API set on Windows.  Use the code in the deprecated directory as a baseline.

When the file is detected, the wrapper will call boinc_temporary_exit() and restart the VM at a later date.

VBOX: Attempt to fix a possible crash seen on T4T with an incompatible version of VirtualBox running on Linux.

VBOX: Try and prevent vboxwrapper from starting the VM if BOINC has signaled boinc_status.quit_requit or boinc_status.no_heartbeat.