while XRenderFillRectangles is not. That's a rather nasty trap for an
unwary Xlib coder like myself. I added batching in chunks of 256
rectangles around XRenderFillRectangles and it started behaving
-precisely like XRenderFillRectangles.
+precisely like XFillRectangles.
Finally, I eliminated some non-determinism from the rectangles test
case. Originally, it was written to choose randomly-sized rectangles