3D support for X11 guests

Our 3D support for X11 guests is a bit of a dilemma for us. There are many, many issues which would be relatively easy to fix. Individually each one might be a day or two's work for a developer. Unfortunately it does not really make sense to address them individually, and just now though of our developers has much time to spend on this. Since a lot of the problems are things which could probably be fixed by users with reasonable 3D development skills, we have decided that for now it makes sense to declare 3D support for X11 guests as "user supported". We will be happy to integrate patches to fix individual problems if we can see without too much effort that they are not going to break other things, and we will be glad to provide other assistance as time permits.

A good approach for many, though not all, issues is to start by creating the smallest possible test application which triggers the problem. As of that point, running the application with debug builds of the 3D guest libraries can help to see what is happening. We are open to suggestions about how we can help without investing too much developer time, and we are also happy to answer questions about how our 3D support works now. Please use the vbox-dev mailing list for this. We would particularly appreciate it if people contributing can document what they learn in a form that we can make publicly available.