0025147: Visualization, TKOpenGl - support EGL as alternative to GLX

Aspect_Window - add interface methods NativeHandle() and NativeParentHandle().
OpenGl_Window - pass OpenGl_GraphicDriver instance to the constructor.
OpenGl_Caps - add option to disable buffers swap at the end of frame redraw.

src/WNT/WNT_Window.cdl

@@ -21,6 +21,7 @@ class Window from WNT inherits Window from Aspect
  uses
 
     Handle             from Aspect,
+    Drawable           from Aspect,
     TypeOfResize       from Aspect,
     NameOfColor        from Quantity,
     Color              from Quantity,
@@ -166,6 +167,14 @@ class Window from WNT inherits Window from Aspect
 	---Purpose: Returns the Windows NT handle parent of the created window <me>.
         ---C++:     inline
 
+    NativeHandle ( me ) returns Drawable from Aspect is virtual;
+    ---Purpose: Returns native Window handle (HWND)
+    ---C++:     inline
+
+    NativeParentHandle ( me ) returns Drawable from Aspect is virtual;
+    ---Purpose: Returns parent of native Window handle (HWND on Windows, Window with Xlib, and so on)
+    ---C++:     inline
+
  fields
 
     aXLeft          : Integer      from Standard is protected; -- Window coordinates

src/WNT/WNT_Window.lxx

@@ -27,3 +27,13 @@ inline Aspect_Handle WNT_Window::HParentWindow() const
 {
   return myHParentWindow;
 }
+
+inline Aspect_Drawable WNT_Window::NativeHandle() const
+{
+  return (Aspect_Drawable )myHWindow;
+}
+
+inline Aspect_Drawable WNT_Window::NativeParentHandle() const
+{
+  return (Aspect_Drawable )myHParentWindow;
+}