Fix 'expand-file-name' during startup on MS-Windows

* src/w32.c (w32_init_file_name_codepage): New function, resets
file_name_codepage and w32_ansi_code_page to undo the values
recorded during dumping.
(codepage_for_filenames): Fix an embarrassing typo.  Ignore the
cached value of file-name encoding if it is nil, i.e. not
initialized yet.  Actually cache the last used file-name encoding
to avoid calling APIs when not necessary.

* src/w32.h (w32_init_file_name_codepage): Add prototype.

* src/w32term.c (syms_of_w32term): Set the value of
w32_unicode_filenames according to the OS version.  This avoids
resetting it during startup, which then causes temacs to run with
the incorrect value.

* src/emacs.c (main): Call w32_init_file_name_codepage early
during the startup.

* src/fileio.c (Fexpand_file_name) [WINDOWSNT]: Update 'newdir'
after converting $HOME to a UTF-8 string, so that 'newdirlim' is
consistent with it.  (Bug#25038)

* lisp/international/mule-cmds.el (set-locale-environment): Set
'default-file-name-coding-system' to the ANSI codepage even in
non-interactive sessions.

* lisp/files.el (directory-abbrev-alist, abbreviated-home-dir):
Doc fix.
(abbreviate-file-name): Decode 'abbreviated-home-dir' if it is a
unibyte string.

* doc/lispref/files.texi (Directory Names): Index
'directory-abbrev-alist'.

lisp/files.el

@@ -51,20 +51,21 @@ when it has unsaved changes."
   nil
   "Alist of abbreviations for file directories.
 A list of elements of the form (FROM . TO), each meaning to replace
-FROM with TO when it appears in a directory name.  This replacement is
-done when setting up the default directory of a newly visited file.
+a match for FROM with TO when a directory name matches FROM.  This
+replacement is done when setting up the default directory of a
+newly visited file buffer.
 
-FROM is matched against directory names anchored at the first
-character, so it should start with a \"\\\\\\=`\", or, if directory
-names cannot have embedded newlines, with a \"^\".
+FROM is a regexp that is matched against directory names anchored at
+the first character, so it should start with a \"\\\\\\=`\", or, if
+directory names cannot have embedded newlines, with a \"^\".
 
 FROM and TO should be equivalent names, which refer to the
-same directory.  Do not use `~' in the TO strings;
-they should be ordinary absolute directory names.
+same directory.  TO should be an absolute directory name.
+Do not use `~' in the TO strings.
 
 Use this feature when you have directories which you normally refer to
 via absolute symbolic links.  Make TO the name of the link, and FROM
-the name it is linked to."
+a regexp matching the name it is linked to."
   :type '(repeat (cons :format "%v"
 		       :value ("\\`" . "")
 		       (regexp :tag "From")
@@ -1736,7 +1737,8 @@ Choose the buffer's name using `generate-new-buffer-name'."
 (make-obsolete-variable 'automount-dir-prefix 'directory-abbrev-alist "24.3")
 
 (defvar abbreviated-home-dir nil
-  "The user's homedir abbreviated according to `directory-abbrev-alist'.")
+  "Regexp matching the user's homedir at the beginning of file name.
+The value includes abbreviation according to `directory-abbrev-alist'.")
 
 (defun abbreviate-file-name (filename)
   "Return a version of FILENAME shortened using `directory-abbrev-alist'.
@@ -1770,8 +1772,23 @@ home directory is a root directory) and removes automounter prefixes
       (or abbreviated-home-dir
 	  (setq abbreviated-home-dir
 		(let ((abbreviated-home-dir "$foo"))
-		  (concat "\\`" (abbreviate-file-name (expand-file-name "~"))
-			  "\\(/\\|\\'\\)"))))
+                  (setq abbreviated-home-dir
+                        (concat "\\`"
+                                (abbreviate-file-name (expand-file-name "~"))
+                                "\\(/\\|\\'\\)"))
+                  ;; Depending on whether default-directory does or
+                  ;; doesn't include non-ASCII characters, the value
+                  ;; of abbreviated-home-dir could be multibyte or
+                  ;; unibyte.  In the latter case, we need to decode
+                  ;; it.  Note that this function is called for the
+                  ;; first time (from startup.el) when
+                  ;; locale-coding-system is already set up.
+                  (if (multibyte-string-p abbreviated-home-dir)
+                      abbreviated-home-dir
+                    (decode-coding-string abbreviated-home-dir
+                                          (if (eq system-type 'windows-nt)
+                                              'utf-8
+                                            locale-coding-system))))))
 
       ;; If FILENAME starts with the abbreviated homedir,
       ;; make it start with `~' instead.