Move rbtree to lib/

That's where it was moved in gfio, one further step towards unifying
the branches.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/fio.h b/fio.h
index 55603cb..e55413a 100644
--- a/fio.h
+++ b/fio.h
@@ -20,7 +20,6 @@
 #include "thread_options.h"
 #include "flist.h"
 #include "fifo.h"
-#include "rbtree.h"
 #include "arch/arch.h"
 #include "os/os.h"
 #include "mutex.h"
@@ -37,6 +36,7 @@
 #include "gettime.h"
 #include "lib/getopt.h"
 #include "lib/rand.h"
+#include "lib/rbtree.h"
 #include "server.h"
 #include "stat.h"
 #include "flow.h"