Custom Handlers for Listers: active

This event indicates that a cache with a custom handler attached has just
become visible.

The message arguments are:-

        Arg0 - "active"            (a string indicating the event type)
        Arg1 - <handle>            (lister handle)
        Arg2 - <title>             (cache title)
        Arg3 - undefined
        Arg4 - <path>              (path of the lister)

Arg2 will contain the custom title of the cache that became active, if it
has been set with  lister set title . If no custom title has been defined,
the path string of the cache is returned instead (ie in this case Arg2 will
be the same as Arg4).