Fix issue with backward iterator of ndimage.

	*  mln/core/image/ndimage_iter.hpp,
	*  mln/core/image/ndimage_pixel_iterator.hpp Fixed.

mln/core/image/ndimage_iter.hpp

@@ -118,7 +118,7 @@ namespace mln
     internal::strided_index_visitor<ndim>,
     pixel_t, internal::deref_return_structure_policy> reverse_iterator;
 
-    typedef iterator const_reverse_iterator;
+    typedef reverse_iterator const_reverse_iterator;
 
 
     ndimage_pixel_range(Image& ima)
@@ -155,7 +155,7 @@ namespace mln
 		      );
     }
 
-    reverse_iterator riter()
+    reverse_iterator riter() const
     {
       typename Image::point_type pmin = ima_->domain().pmin;
       typename Image::point_type pmax = ima_->domain().pmax;

mln/core/image/ndimage_pixel_iterator.hpp

@@ -61,9 +61,9 @@ struct ndimage_pixel_range
     {
       Image::point_type pmin = ima_->domain().pmin;
       Image::point_type pmax = ima_->domain().pmax;
-      return iterator(pixel_t(ima_),
-		      internal::make_point_visitor(pmax - pmin),
-		      internal::strided_pointer_value_visitor<ndim>(ima->last_, strides.begin()));
+      return reverse_iterator(pixel_t(ima_),
+                              internal::make_point_visitor(pmax - pmin),
+                              internal::strided_pointer_value_visitor<ndim>(ima->last_, strides.begin()));
     }
 
   private: