bug#30955: 27.0.50; Mouse clicks on header-line in Info are broken

[Eli Zaretskii <eliz@gnu.org>]

To reproduce:

  emacs -Q
  C-u C-h i /path/to/info/elisp.info RET
  2
  3
  4
  Click mouse-1 on the "Up: Programming Types" link on the header-line

This results in an error:

  <header-line> <header-line> <mouse-2> is undefined

If you now type "C-h c" followed by the same mouse-1 click, you will
see

  <header-line> <down-mouse-1> (translated from <down-mouse-1>) at that spot runs the command mouse-drag-header-line

as expected, but before that, momentarily, the echo area will flash
this:

  header-line header-line mouse-2-

Reverting the following commit fixes the problem:

  commit 3d5e31eceb9dc1fb62b2b27bcab549df3bd04ce9
  Author:     Stefan Monnier <monnier@iro.umontreal.ca>
  AuthorDate: Tue Jan 30 12:41:29 2018 -0500
  Commit:     Stefan Monnier <monnier@iro.umontreal.ca>
  CommitDate: Tue Jan 30 12:41:29 2018 -0500

      * lisp/mouse.el: Rework the mouse-1-click remapping

      Avoid peeking ahead at the next event because this had undesirable effects,
      such as making 'this-single-command-raw-keys' return bogus information.

      (mouse--last-down): New variable.
      (mouse--down-1-maybe-follows-link): Don't do the remapping here.
      Instead, just keep track of the time when the down happened.
      (mouse--down-1-maybe-follows-link): Do the remapping here.
      (key-translation-map): Add bindings for (double-)mouse-1.


In GNU Emacs 27.0.50 (build 169, i686-pc-mingw32)
 of 2018-03-25 built on HOME-C4E4A596F7
Repository revision: 1be6a21fd8b5ade67f7f69f964331aa570623683
Windowing system distributor 'Microsoft Corp.', version 5.1.2600
Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
<header-line> <header-line> <mouse-2> is undefined

Configured using:
 'configure --prefix=/d/usr --enable-checking=yes,glyphs --with-wide-int
 --with-modules --enable-check-lisp-object-type 'CFLAGS=-O0 -gdwarf-4
 -g3''

Configured features:
XPM JPEG TIFF GIF PNG RSVG SOUND NOTIFY ACL GNUTLS LIBXML2 ZLIB
TOOLKIT_SCROLL_BARS MODULES THREADS JSON LCMS2

Important settings:
  value of $LANG: ENU
  locale-coding-system: cp1255

Major mode: Info

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  buffer-read-only: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny seq byte-opt gv
bytecomp byte-compile cconv dired dired-loaddefs format-spec rfc822 mml
mml-sec password-cache epa derived epg epg-config gnus-util rmail
rmail-loaddefs mm-decode mm-bodies mm-encode mail-parse rfc2231
mailabbrev gmm-utils mailheader cl-loaddefs cl-lib sendmail rfc2047
rfc2045 ietf-drums mm-util mail-prsvr mail-utils info easymenu time-date
elec-pair mule-util tooltip eldoc electric uniquify ediff-hook vc-hooks
lisp-float-type mwheel dos-w32 ls-lisp disp-table term/w32-win w32-win
w32-vars term/common-win tool-bar dnd fontset image regexp-opt fringe
tabulated-list replace newcomment text-mode elisp-mode lisp-mode
prog-mode register page menu-bar rfn-eshadow isearch timer select
scroll-bar mouse jit-lock font-lock syntax facemenu font-core
term/tty-colors frame cl-generic cham georgian utf-8-lang misc-lang
vietnamese tibetan thai tai-viet lao korean japanese eucjp-ms cp51932
hebrew greek romanian slovak czech european ethiopic indian cyrillic
chinese composite charscript charprop case-table epa-hook jka-cmpr-hook
help simple abbrev obarray minibuffer cl-preloaded nadvice loaddefs
button faces cus-face macroexp files text-properties overlay sha1 md5
base64 format env code-pages mule custom widget hashtable-print-readable
backquote w32notify w32 lcms2 multi-tty make-network-process emacs)

Memory information:
((conses 16 132974 9857)
 (symbols 56 21395 1)
 (miscs 48 58 152)
 (strings 16 36869 2443)
 (string-bytes 1 867215)
 (vectors 16 15422)
 (vector-slots 8 580149 18798)
 (floats 8 59 58)
 (intervals 40 4939 217)
 (buffers 880 13))