1. cluster seems to have a memory leak, put DESTROY functions in where

1. cluster seems to have a memory leak, put DESTROY functions in where
appropriate.
2. try to make sure that PC21 commands are not issued inappropriately and
also reformat PC19 for onward broadcast so that nodes coming in on loops are
dropped from those broadcasts.
3. make sure PC16,17,19,21 doen't affect locally connected nodes.