Fix for x11vnc problems on Stretch

Following up to my last article, having tested x11vnc for a day on mediapc, it crashed with the “stack smashing detected” issue. Reported as a Debian bug here:

This issue affects multiple distros, including ones unrelated to Debian, such as Red Hat, Arch and Fedora, as well as related such as Ubuntu.
The recommended solution for Debian Stretch is to install the x11vnc packages from the testing repository. I have now applied them to mediapc for further evaluation.
Hopefully this will make x11vnc reliable enough to be used for my purposes. This is about the first update to x11vnc in eight years.