Fix missing format when writing Algorithm-based objects

Added a writeFormat() method to Algorithm which must be called by the
write() method of derived classes.

modules/shape/src/aff_trans.cpp

@@ -79,6 +79,7 @@ public:
     //! write/read
     virtual void write(FileStorage& fs) const
     {
+        writeFormat(fs);
         fs << "name" << name_
            << "affine_type" << int(fullAffine);
     }