Update the server code to eliminate the need for a 5-second delay when
attempting to terminate a client connection from within an operation plugin.
The issue arose when the attempt to terminate the connection tried to cancel
the operation that initiated the disconnect, which made it necessary to wait
for a 5-second timeout before continuing.

This solution also creates a new PluginOperation interface that is the
superclass for the PreParseOperation, PreOperationOperation, 
PostOperationOperation, and PostResponseOperation interfaces.

OpenDS Issue Number:  784