0026732: Visualization, TKOpenGl - add option to request Core profile 3.2+ using GLX

0026732: Visualization, TKOpenGl - add option to request Core profile 3.2+ using GLX

Aspect_Window::NativeFBConfig() - extend interface with new method.
Xw_Window - add Aspect_FBConfig option to constructors,
use glXChooseFBConfig() instead of glXChooseVisual() on GLX1.3+.

OpenGl_Window - create context using glXCreateContextAttribsARB()
when GLXFBConfig is provided by Aspect_Window.
This procedure now handles Core Profile and Debug Context options on Linux.

OpenGl_Window - drop code implicitly creating child window
when window XVisual is incomplete for OpenGL context.
This should eliminate event-handling issues at application side,
but would require window to be properly created by application.