#232: resurrect the "point sprites for runway lights" switch

Automatic GL/OSG feature detection still not working, since we don't have
a "context" - but at least the manual switch works (on start-up only).

simgear/scene/tgdb/pt_lights.cxx

@@ -204,6 +204,10 @@ Effect* getLightEffect(float size, const Vec3& attenuation,
     Pass *combinedPass = clone(spritePass, CopyOp::SHALLOW_COPY);
     combinedPass->setAttributeAndModes(point);
     Effect* effect = new Effect;
+    std::vector<std::string> parameterExtensions;
+
+    if (SGSceneFeatures::instance()->getEnablePointSpriteLights())
+    {
         std::vector<std::string> combinedExtensions;
         combinedExtensions.push_back("GL_ARB_point_sprite");
         combinedExtensions.push_back("GL_ARB_point_parameters");
@@ -217,8 +221,9 @@ Effect* getLightEffect(float size, const Vec3& attenuation,
         spriteTniq->passes.push_back(spritePass);
         spriteTniq->setGLExtensionsPred(2.0, spriteExtensions);
         effect->techniques.push_back(spriteTniq);
-    std::vector<std::string> parameterExtensions;
         parameterExtensions.push_back(combinedExtensions.back());
+    }
+
     Technique* parameterTniq = new Technique;
     parameterTniq->passes.push_back(attenuationPass);
     parameterTniq->setGLExtensionsPred(1.4, parameterExtensions);

simgear/scene/util/SGSceneFeatures.hxx

@@ -46,6 +46,10 @@ public:
 
   void setEnablePointSpriteLights(bool enable)
   { _pointSpriteLights = enable; }
+  bool getEnablePointSpriteLights() const
+  {
+      return _pointSpriteLights;
+  }
   bool getEnablePointSpriteLights(unsigned contextId) const
   {
     if (!_pointSpriteLights)