Fixed race condition in MongoAsyncQueryCursor when exhaust flag is set.
Added ServerConnection sub-interface of Connection, from which you can retrieve the ServerDescription.  This will be necessary to do things like apply the max message size or enforce the max document size.
Added AsyncServerConnection sub-interface of AsyncConnection, from which you can retrieve the ServerDescription.  This will be necessary to do things like apply the max message size or enforce the max document size.
All operation class now take ServerConnection/AsyncServerConnection.
MongoRequestMessage.encodeMessageBody now takes a ServerDescription
MongoInsertMessage now enforces max message size as specified in the server description.