Read directory name, prompting with PROMPT and completing in directory DIR.
Value is not expanded---you must call `expand-file-name' yourself.
Default name to DEFAULT-DIRNAME if user exits with the same
non-empty string that was inserted by this function.
(If DEFAULT-DIRNAME is omitted, DIR combined with INITIAL is used,
or just DIR if INITIAL is nil.)
If the user exits with an empty minibuffer, this function returns
an empty string. (This can only happen if the user erased the
pre-inserted contents or if `insert-default-directory' is nil.)
Fourth arg MUSTMATCH non-nil means require existing directory's name.
Non-nil and non-t means also require confirmation after completion.
Fifth arg INITIAL specifies text to start with.
DIR should be an absolute directory name. It defaults to
the value of `default-directory'.