Implement blueprint: 'feature-feeder-in-core'.

Replicator was updated:
 - bind replicator poer strategy was changed.
 - terminate child routine for spawner process during exit was added.
 - handle EPIPE error was added to client handler process.
 - remote_hot_standby was deleted.
 - local_hot_standby was renamed to hot_standby.
 - sender_send_sock function was fixed.
 - I/O event processing in replicator fibers was updated.

Fiber:
 - fiber_io_* functions now public.