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.

TODO: Refactor how command line options and vbox_job.xml options are handled.  This was a ugly hack.