Add rw_sequencer option

Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
diff --git a/ioengine.h b/ioengine.h
index ff3069b..389e95a 100644
--- a/ioengine.h
+++ b/ioengine.h
@@ -8,6 +8,7 @@
 	IO_U_F_FLIGHT		= 1 << 1,
 	IO_U_F_FREE_DEF		= 1 << 2,
 	IO_U_F_IN_CUR_DEPTH	= 1 << 3,
+	IO_U_F_BUSY_OK		= 1 << 4,
 };
 
 /*