TCP hardlimits

fixes #326 (closed)

Several bugs fixed:

• TCP client count can be limited by the config variable max_tcp_clients in system (so there are free descriptors for autonomous operation)
• Aggressive limits when client connects, but doesn't start sending data in time
• Throttling doesn't affect activity other then accept()
• Possible resource leak on tcp_sweep
• Bad logic (started reading from socket before checking for error activity first)
• Bad logic (could close master socket on fd exhaustion)

Also merge to master.