[#19258] [patch] Adding drawing capabilities to BGE Python

patch from Mitchell Stokes (moguri)

simple use case
 scene.post_draw = [pyOpenGLFunc]

this only needs to be set once, then the funcion runs each redraw.

note, this patch also changes how python scripts run (not modules): Dont clear the namespace after running a script, since functions still use the namespace, BGE API is now better when dealing with stale data.

made some changes to this patch.
- assigning a list didnt decrement the existing list.
- initialize as NULL rather then a blank list
- dont use string comparisons for the callbacks, pass the python list to use instead.
- dont check the list items are callable. python will display an error if they are not.
- use python list macros that dont do any type checking sine blender does this when assigning the list

---- from tracker, edited since an updated patch changes some things.
Here is a patch to be able to draw to the screen with BGE Python. This will be very handy for GUI stuff. This patch
works by having the user register a callback in the scene. Two options are available KX_Scene.pre_draw
and KX_Scene.post_draw. The difference between these is when Python draws to the screen (before or after the BGE).
Each can take a list of functions. Here is an example that draws a blue semi-transparent

source/gameengine/GameLogic/SCA_PythonController.cpp

@@ -465,7 +465,8 @@ void SCA_PythonController::Trigger(SCA_LogicManager* logicmgr)
 	{
 		/* clear after PyErrPrint - seems it can be using
 		 * something in this dictionary and crash? */
-		PyDict_Clear(excdict);
+		// This doesn't appear to be needed anymore
+		//PyDict_Clear(excdict);
 		Py_DECREF(excdict);
 	}