Made the requirement that the two images be different objects

a little more clear.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%403980

dlib/image_transforms/spatial_filtering.h

@@ -38,7 +38,7 @@ namespace dlib
             "\tvoid spatially_filter_image()"
             << "\n\tYou can't give a scale of zero"
             );
-        DLIB_ASSERT((void*)&in_img != (void*)&out_img ,
+        DLIB_ASSERT(is_same_object(in_img, out_img),
             "\tvoid spatially_filter_image()"
             << "\n\tYou must give two different image objects"
             );

dlib/image_transforms/spatial_filtering_abstract.h

@@ -28,7 +28,7 @@ namespace dlib
             - out_image_type == is an implementation of array2d/array2d_kernel_abstract.h
             - pixel_traits<typename in_image_type::type>::has_alpha == false
             - pixel_traits<typename out_image_type::type>::has_alpha == false 
-            - &in_img != &out_img
+            - is_same_object(in_img, out_img) == false 
             - scale > 0
             - M % 2 == 1  (i.e. M must be odd)
             - N % 2 == 1  (i.e. N must be odd)