Merge of r4416: Fixed AIO error handling on FreeBSD. The aio_return() must be called regardless of the error returned by aio_error(). Not calling it resulted in various problems up to segmentation faults (as AIO events are level-triggered and were reported again and again). Additionally, in "aio sendfile" case r->blocked was incremented in case of error returned from ngx_file_aio_read(), thus causing request hangs.