Fixed compiler warnings (and potential memory issues)

git-svn-id: svn+ssh://svn.code.sf.net/p/supertuxkart/code/main/branches/irrlicht@3679 178a84e3-b1eb-0310-8ba1-8eac791a3b58

src/animations/animation_base.cpp

@@ -21,4 +21,4 @@
 
 void AnimationBase::update(float dt)
 {
-}   // float dt
+}   // float dt

src/animations/animation_base.hpp

@@ -43,6 +43,8 @@ private:
 
 public:
 	AnimationBase() {}
+    virtual ~AnimationBase(){}
+
 
 	virtual void update(float dt);
 

src/animations/billboard_animation.hpp

@@ -31,6 +31,8 @@ private:
 
 public:
 	BillboardAnimation(const XMLNode &node);
+    virtual ~BillboardAnimation(){}
+
 
 };   // BillboardAnimation
 

src/animations/three_d_animation.hpp

@@ -31,6 +31,7 @@ private:
 
 public:
 	ThreeDAnimation(const XMLNode &node);
+    virtual ~ThreeDAnimation(){}
 
 };   // ThreeDAnimation
 #endif

src/graphics/nitro.hpp

@@ -37,7 +37,7 @@ private:
     scene::IParticleEmitter         *m_emitter;
 public:
                  Nitro          (Kart* kart);
-                ~Nitro          ();
+    virtual     ~Nitro          ();
     virtual void update         (float t);
     void         setCreationRate(float f);
 };