* src/misc/formater.hh: Add virtual destructors to please g++-4.0.

src/misc/formater.hh

@@ -29,9 +29,10 @@ namespace spot
   class printable
   {
   public:
-    ~printable()
+    virtual ~printable()
     {
     }
+
     virtual void
     print(std::ostream&, const char*) const = 0;
   };
@@ -112,6 +113,10 @@ namespace spot
       call_['%'] = call_[0] = &percent;
     }
 
+    virtual ~formater()
+    {
+    }
+
     /// Collect the %-sequences occurring in \a fmt.
     void
     prime(const char* fmt);