Don't require dlopen, but link to ole32 and oleaut32 on Windows.

Don't expose g_pVBoxFuncs anymore. It was only used to get the
version of the API. Make VBoxCGlueInit return the version instead.
This simplifies the implementation of the MSCOM glue layer.

Get the VirtualBox version from the registry.

Add a dummy implementation of the nsIEventQueue to the MSCOM glue
as there seems to be no direct equivalent with MSCOM. It might be
implemented using the normal window message loop. This requires
additional investigation.