opengl exception handler function

[Antoine Martin]

Follow up from #1769: register a callback function on the opengl context object to reset the context when we encounter an error, so that later screen updates will succeed.

[Antoine Martin]

Not easy.
There are two parts: the window backing context and the underlying opengl context (ie: GLX context).
We can't re-initialize the latter without also re-initializing the former.
Another problem is that some paint functions already catch and handle exceptions, so the code would need to be added to each one of those rather than doing it generically in the gl-context object.

[Antoine Martin]

example glcontext re-init handler