Register the virtual key command for the right control key.

This fixes a load error I was receiving due to the change made in 839ccb1a22d0c0e70cf76922c356882ba668d5ca.  Since "Control_R" wasn't a defined typeable key, dragonfly would fail to load the grammar properly.

Note I wasn't able to test this out, but the grammar loads now and it seems to be doing the same thing dragonfly does in defining its key bindings.