BGE: Finally adding support for additive layer blending.

Currently this is only for the Python API. The logic brick will be updated in a future commit.

source/gameengine/Ketsji/KX_PythonInit.cpp

@@ -1820,6 +1820,10 @@ PyObject *initGameLogic(KX_KetsjiEngine *engine, KX_Scene* scene) // quick hack
 	KX_MACRO_addTypesToDict(d, KX_ACTION_MODE_LOOP, BL_Action::ACT_MODE_LOOP);
 	KX_MACRO_addTypesToDict(d, KX_ACTION_MODE_PING_PONG, BL_Action::ACT_MODE_PING_PONG);
 
+	/* BL_Action blend modes */
+	KX_MACRO_addTypesToDict(d, KX_ACTION_BLEND_BLEND, BL_Action::ACT_BLEND_BLEND);
+	KX_MACRO_addTypesToDict(d, KX_ACTION_BLEND_ADD, BL_Action::ACT_BLEND_ADD);
+
 	// Check for errors
 	if (PyErr_Occurred())
 	{