Fixed failure path in pool growing route. Do not grow non-blocking IO pool at all - this is not needed anymore after srw processing stopped blocking, and started postponing ack sending.
Do not use app_watcher blocking helper - enqueue directly. It works, since we do not send ack for blocking requests until it is processed - ack (or data) will be sent in job's destructor
Removed app_watcher class
Removed dead code
Elliptics version update: 2.20.2.0
Do not allow to start the same engine again