Channel example worker to worker fix, minor fixes for other examples

[hunhoffe]

The channel example for worker to worker previously did not work. In addition to the lack of functionality, a known limitation of the old design was that it only worked for when an image was broken up into a 2x2 set of data tiles.

I decided to go through it and spend more time on checking the design, as well as relaxing that limitation. I did that, and I found another error besides, and fixed the example.

However, the example is still a little brittle so I created an issue to address this.