Added protected d-tor to sf::NonCopyable to prevent possible resource leaks.

Author: eXpl0it3r

include/SFML/System/NonCopyable.hpp

@@ -51,6 +51,16 @@ class SFML_SYSTEM_API NonCopyable
     ///
     ////////////////////////////////////////////////////////////
     NonCopyable() {}
+    
+    ////////////////////////////////////////////////////////////
+    /// \brief Default destructor
+    ///
+    /// By declaring a protected destructor it's impossible to
+    /// call delete on a pointer of sf::NonCopyable, thus
+    /// preventing possible resource leaks.
+    ///
+    ////////////////////////////////////////////////////////////
+    ~NonCopyable() {}
 
 private: