Upgrading to VirtualBox 5

[Warren Block]

Before upgrading to the new VirtualBox 5 port, check UPDATING and back 
up existing VMs.

Attempting to run an old VM without unloading the old VirtualBox kernel 
module (vboxdrv) and loading the new version produces this error:

   RTR3InitEx failed with rc=-1912(rc=-1912)

   where: supR3HardenedMainInitRuntime what: 4
   VERR_VM_DRIVER_VERSION_MISMATCH (-1912) - The installed
   support driver doesn't match the version of the user.

'kldunload vboxdrv && kldload vboxdrv' *should* work, but the error 
might prevent that and require a reboot to load the new version.

After getting the new kernel module loaded, update the Guest Additions 
in the VMs.