Set scratchpad_state to changed if floating.

Long description:

If the window is floating when moved to scratchpad, set the state to
changed so that it isn't resized and centered when it is shown.

To apply this patch, use:
curl http://cr.i3wm.org/patch/8/raw.patch | git am

@@ -49,6 +49,9 @@ void scratchpad_move(Con *con) {

         con = con->parent;

     } else {

         con = maybe_floating_con;

+        if (con->scratchpad_state == SCRATCHPAD_NONE) {

+            con->scratchpad_state = SCRATCHPAD_CHANGED;

+        }

     }

     /* 2: Send the window to the __i3_scratch workspace, mainting its