Storing Light position as Vector4, not Vector3.

Four bytes more, but more convenient when multiplying with camera
matrix.

src/Light.cpp

@@ -19,7 +19,7 @@ namespace Magnum {
 
 void Light::setClean() {
     if(!isDirty()) return;
-    _position = absoluteTransformation().at(3).xyz();
+    _position = absoluteTransformation().at(3);
     Object::setClean();
 }
 

src/Light.h

@@ -39,7 +39,7 @@ class Light: public Object {
         /**
          * @brief Light position relative to root object (scene)
          */
-        inline Vector3 position() {
+        inline Vector4 position() {
             setClean();
             return _position;
         }
@@ -50,7 +50,7 @@ class Light: public Object {
         void setClean();
 
     private:
-        Vector3 _position;
+        Vector4 _position;
 };
 
 }