Comment 14 for bug 1351597

I have a possible way to fix this bug.

What I noticed is that Inkscape queues redraws to the canvas by using `gdk_threads_add_idle_full` at `src/display/sp-canvas.cpp:2332`, in contrast, `sp_ruler_draw_pos` in `src/widgets/ruler.cpp` is called directly from within the mouse signal handler.

This patch changes `sp_ruler_draw_pos` to be called by queuing the function with `gdk_threads_add_idle_full`.

Tested this with 0.91 64-bit under Windows 7, with Intel HD Graphics 4000

This patch, however, causes another minor rendering bug when dragging the drawing area around very quickly. I guess this has something to do with priorities also.