Adds a child to the list of nodes to which this node
has already send a implicit HeartBeat message in the form of
Publish message in this Heartbeat period.
An application can create sub-classes of MessageAnycast type of
messages and write their own handling functions so as to do
some application-specific predicate searching.
An application can create sub-classes of MessageAnycast type of
messages and write their own handling functions so as to take care
of routing of these messages and also to handle cases where the
anycast message reaches an
intermediate node where there is no application running to take care
of it.