bug#22144: --exclude no longer works against arguments with a directory name

[Paul Eggert]

Vincent Lefevre wrote:
> How is the file name defined, then?

It's built as a string, which is passed to 'open' without worrying about 
realpath.

By the way in case it's not already clear, I agree with you that the current 
behavior is not good, it's just that we can't simply revert (as that was also 
not good), we need to make it better.