The logic of StreamManagementIOProcessor::shouldRequestAck() was modified to follow this rules:

• sending <r/> only for X unacked stanzas after the previous <r/> request sent to the client If ack_request_count is set to 10, then for 100 messages sent in a batch, it would result in 10 <r/> sent (assuming no. <a/> was received during this time).
• sending <r/> only if it was not sent in the last X milliseconds and if during this time no <a/> was received This would even further reduce no. of requests sent for stanzas sent in a batch as by default it would send only a single <r/> for all stanzas in a batch which were sent in 200ms (ack_request_min_delay is configurable property).

By setting ack_request_min_delay to 0, the server would use only the stanza counter for estimating when it should send requests. By setting also ack_request_count to 1, the server would be again sending <r/> for each sent stanza.

This new code is available in a feature branch and PR was created at https://github.com/tigase/tigase-server/pull/150

@wojtek Please review this logic and code before we merge this to master.

I reviewed the code and it looks ok. Added a couple minute comments. Please also include this in the documentation (could be based on your comment above)