Salvage a VirtualBox machine you forgot to export

If you copy the data files of a VirtualBox machine to another PC without exporting it as an .ova appliance first, it's painful to get it into another VirtualBox installation. Thankfully there is a workaround:

• Create a new machine
• Copy the .vdi drive data into the new machine folder
• In the machine settings, add that .vdi as a hard drive, and remove the dummy .vdi you created when creating that machine.