Move rbtree into lib/

And make ARRAY_SIZE() generally available, also outside gfio.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/gfio.c b/gfio.c
index e4d1f21..274dea8 100644
--- a/gfio.c
+++ b/gfio.c
@@ -1389,7 +1389,7 @@
 	gtk_container_add(GTK_CONTAINER(bottom_align), ge->buttonbox);
 	gtk_box_pack_start(GTK_BOX(main_vbox), bottom_align, FALSE, FALSE, 0);
 
-	add_buttons(ge, buttonspeclist, ARRAYSIZE(buttonspeclist));
+	add_buttons(ge, buttonspeclist, ARRAY_SIZE(buttonspeclist));
 
 	/*
 	 * Set up thread status progress bar