Added missing virtual destructors

Author: andreagilardoni

api/Print.h

@@ -43,6 +43,8 @@ class Print
     void setWriteError(int err = 1) { write_error = err; }
   public:
     Print() : write_error(0) {}
+    virtual ~Print() {}
+
 
     int getWriteError() { return write_error; }
     void clearWriteError() { setWriteError(0); }

api/Printable.h

@@ -34,6 +34,7 @@ class Print;
 class Printable
 {
   public:
+    virtual ~Printable() {}
     virtual size_t printTo(Print& p) const = 0;
 };