Bugfix: Lock participants while distributing a datagram.
We don't want to delete a participant if we're waiting to iterate over it.
Revert "Bugfix: Lock participants while distributing a datagram."

It can lead to dead locks in current and future implementations.
This reverts commit db1868d34114ac501ffdcfb4a30a01776786375d.
Deletes should not occur while routing messages.
Properly initialize the m_is_terminated flag on MDParticipant.
ClientAgent: Don't forward messages if Client is terminated.
ClientAgent: Client should clean itself up before calling terminate.
Merge pull request #274 from Astron/bugfix/pure-virtual-participant

Bugfix: Client pure virtual method call