Replaced Aliased OpenGLExtensionCalls

replaced glCalls which used Extensions, that are aliased following OpenGL Specification.

relates to https://www.graphics.rwth-aachen.de:9000/OpenFlipper-Free/OpenFlipper/issues/5 and https://www.graphics.rwth-aachen.de:9000/OpenFlipper-Free/OpenFlipper-Free/issues/27

I used a small powershell script to parse the OpenGL Spec gl.xml The script consists of less than 30 Lines of Code, and downloads the spec from github and deletes it afterwards. I also challenged @kschuster to do the same using python. Excited to see his results.

You judge who wins by merging the respective MR

DepthPeeling.cc

@@ -743,7 +743,7 @@ void DepthPeeling::renderDualPeeling(ACG::GLState* _glState, Viewer::ViewerPrope
       // blend back color into accumulation buffer
       glDrawBuffer(colorBlendTarget);
 
-      glBlendEquationEXT(GL_FUNC_ADD);
+      glBlendEquation(GL_FUNC_ADD);
       ACG::GLState::blendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
 
       // bind back color texture to slot 0