Made Filestorage able to not own its CvFileStorage instance.

This allows to get rid of the last remaining Ptr<T>::addref calls.

modules/objdetect/src/hog.cpp

@@ -1353,8 +1353,7 @@ public:
     {
         if(ptr && _fs)
         {
-            FileStorage fs(_fs);
-            fs.fs.addref();
+            FileStorage fs(_fs, false);
             ((const _ClsName*)ptr)->write(fs, String(name));
         }
     }