directory_completion_hook interacts with tilde expansion

[stefanholek]

When a directory_completion_hook is set, readline always tilde-expands filenames. This means we lose the ability to "set expand-tilde off".

[stefanholek]

Here's what the readline maintainers say:

"That's up to the application. The calling application has complete freedom
to change the directory name -- there's no guarantee that the original
pathname with the tilde is related to the rewritten directory name, which
readline is going to open and search for matches. You can't guarantee
that adding the original name, complete with tilde, back to the list of
matches will result in valid pathnames."