1. Export fps related API so that subsystem implementation no longer need to know about details in encoder structure.
2. Discard frameList dictionary.
The 'value' in this dictionary is never used and not properly free'ed when client is disconnected.
The dictionary was used to calculate 'inflight' frame count. Once an ACK is received from client, an item in the dictionary is removed.
We then calculate 'inflight' frame by the count of the items in the dictionary.
However, some rdp clients (win7 mstsc) skips frame ACK if it is inactive, ACK of some frame would actually never arrive.
We actually don't need the dictionary. We only need to record the latest acknowledged frame id, and the difference between last sent frame id is the inflight frame count.
3. Minor fix in default fps calculation. encoder->frameAck is wrongly used as integer while it's actually bool flag.
1. Introduce message queue in shadow client. No longer use subsytem->MsgPipe->out to deliver message to clients.
We used to use subsytem->MsgPipe->out for messages which need to be sent to client. But it's not correct. Only one client would get the message if multiple client exists
This problem make the fix in PR #2643 incomplete.
Introduced reference count based solution to release resource taken by the message.
Also added APIs for client message delivery.
Also fixed msg pipe in subsystem to clean resource when destroyed.
2. Discard unused StopEvent in client. We actually use quit message instead.
3. Enhance disposal of channels.
Free context for remdesk and encomsp channels. The original fix only stop the threads, but doesn't release resource.
Dispose channels earlier. The channels are built on client->vcm. Disposing channels after client->vcm is closed cause unknown behavior.
Original fix is #2644
4. Start to add audio support.
