Add support for limiting only rate in only one direction

So now you can say 'limit writes to 10MB/sec' and have reads go
full throttle, for instance.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/ioengine.h b/ioengine.h
index 18496c3..9c0ed9a 100644
--- a/ioengine.h
+++ b/ioengine.h
@@ -140,8 +140,8 @@
 extern struct io_u *get_io_u(struct thread_data *);
 extern void put_io_u(struct thread_data *, struct io_u *);
 extern void requeue_io_u(struct thread_data *, struct io_u **);
-extern long __must_check io_u_sync_complete(struct thread_data *, struct io_u *);
-extern long __must_check io_u_queued_complete(struct thread_data *, int);
+extern int __must_check io_u_sync_complete(struct thread_data *, struct io_u *, unsigned long *);
+extern int __must_check io_u_queued_complete(struct thread_data *, int, unsigned long *);
 extern void io_u_queued(struct thread_data *, struct io_u *);
 extern void io_u_log_error(struct thread_data *, struct io_u *);
 extern void io_u_mark_depth(struct thread_data *, unsigned int);