Add virtual destructor for MultiTask. Reason: To be able to

delete derived objects using MultiTask *.


git-svn-id: https://svn.microneil.com/svn/CodeDweller/branches/adeniz_1@104 d34b734f-a00e-4b39-a726-e4eeb87269ab

multitasking.hpp

 class MultiTask {
   public:
     enum class State{Running, Waiting, Finished};
+    virtual ~MultiTask() {}
     virtual State task() = 0;
 };