Custom Handlers for Listers: root

A root event will be received when the Root Directory item is chosen
from the lister cache pop-up menu, or whenever the user uses the root
hot key, ":".

The message arguments are:-

        Arg0 - "root"              (a string indicating the event type)
        Arg1 - <handle>            (source lister handle)
        Arg2 - <path>              (path of lister)
        Arg3 - undefined
        Arg4 - undefined
        Arg5 - undefined
        Arg6 - <qualifiers>        (string indicating qualifiers pressed
                                   - only shift keys)