Suggestion from Dan Jacobson.
The sentence or two describing the common case must appear just once,
and then it must be made to appear in the 70+ places where it's needed.
+
+du: rewrite to use something other than nftw to perform directory traversal.
+ Due to design limitations of nftw, ...
+ using -D makes du dereference each command
+ line argument that is a symlink to a directory.
+ A symlink to non-directory is not dereferenced.