Heretic II also installs, by default, a symlink called libGL.so in
the application directory. You can remove or rename this symlink, since
the system will then find the default libGL.so (which our
drivers install in /usr/lib). From within Heretic II you
can then set your render mode to OpenGL in the video menu.
There is also a patch available to Heretic II from lokigames at: