Allow 3-tuples to pass through as predefined entry.

I would like to be able to pass the following through in configuration:

    {[erlang,memory],
     {function, erlang, memory, ['$dp'], value,
      [total,processes,ets,binary,atom,atom_used,maximum]},
     []
    }

This patch is intended to allow this.

Signed-off-by: Brian L. Troutwine <brian.troutwine@adroll.com>