Allow readwrite as an alias for rw in setting sequential read/write

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/options.c b/options.c
index 3de0221..f8927ee 100644
--- a/options.c
+++ b/options.c
@@ -944,6 +944,10 @@
 			    .oval = TD_DDIR_RW,
 			    .help = "Sequential read and write mix",
 			  },
+			  { .ival = "readwrite",
+			    .oval = TD_DDIR_RW,
+			    .help = "Sequential read and write mix",
+			  },
 			  { .ival = "randrw",
 			    .oval = TD_DDIR_RANDRW,
 			    .help = "Random read and write mix"