Replace nonprinting characters in directory with printable representations.
The printable representations use ^ (for ASCII control characters) or hex.
The characters tab, linefeed, space, return and formfeed are not affected.
Interactively, the command prompts for a directory and a file name regexp for
matching.
Noninteractively, if DIR is nil, prompts for DIRectory. If FILE-REGEXP is nil,
prompts for FILE(name)-REGEXP.
See also documentation for `pr-list-directory'.
(fn &optional DIR FILE-REGEXP)