Fix documentation and implementation of 'directory-name-p'

* lisp/files.el (directory-name-p): Modify to recognize
backslashes on MS-Windows and MS-DOS.  Adjust the doc string
accordingly.  Use '=', not char-equal, for comparison, as
letter-case cannot possibly be an issue here.

* doc/lispref/files.texi (Directory Names): Move the documentation
of directory-name-p here from "Relative File Names".  Update the
description per the changes in implementation.

* etc/NEWS: Move the entry for 'directory-name-p' to its proper
place and mark it documented.

1 files changed, 7 insertions, 5 deletions

diff --git a/etc/NEWS b/etc/NEWS
index bd7435b1760..fa43a7f9f6a 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -181,11 +181,6 @@ for use in Emacs bug reports.
 hiding character but the default `.' can be used by let-binding the
 variable `read-hide-char'.
 
-** The new function `directory-name-p' can be used to check whether a file
-name (as returned from, for instance, `file-name-all-completions' is
-a directory file name.  It returns non-nil if the last character in
-the name is a forward slash.
-
 ** The function `font-info' now returns more details about a font.
 In particular, it now returns the average width of the font's
 characters, which can be used for geometry-related calculations.
@@ -1302,6 +1297,13 @@ integers.
 ** New function `set-binary-mode' allows to switch a standard stream
 of the Emacs process to binary I/O mode.
 
++++
+** The new function `directory-name-p' can be used to check whether a file
+name (as returned from, for instance, `file-name-all-completions') is
+a directory file name.  It returns non-nil if the last character in
+the name is a directory separator character (forward slash on GNU and
+Unix systems, forward- or backslash on MS-Windows and MS-DOS).
+
 ** ASCII approximations to curved quotes are put in standard-display-table
 if the terminal cannot display curved quotes.