Make it unbootable on (X)Wayland and Wayback

[darkhog]

It is important that people are directed to the proper TuWiM/TWM environment (X11) to avoid any potential issues that would get unjustly blamed on this software. Therefore it is critical to figure out a way to stop TuWiM from working on XWayland and Wayback. Ideally, it should fail gracefully, with an error message in the terminal pointing the user towards using TuWiM in a proper X environment such as Xorg or Xlibre.

Please feel free to share ways to detect XWayland or Wayback usage so that TuWiM can gracefully fails in such unsupported and function-less environment.

[Consolatis]

First of all: yay for anti-features.
Second: WAYLAND_DISPLAY and WAYLAND_SOCKET should work for anything other than Wayback. Potentially also XDG_SESSION_TYPE.