bugs related to tabs

[Katsumi Yamaoka <yamaoka@xxxxxxx>]

This bug report will be sent to the emacs-w3m development team,
 not to your local site managers!!
Please write in simple English, because the emacs-w3m developers
aren't good at English reading. ;-)

Please describe as succinctly as possible:
	- What happened.
	- What you thought should have happened.
	- Precisely what you were doing at the time.

Please also include any Lisp back-traces that you may have.
================================================================
Dear Bug Team!

  There are at least three serious bugs related to tabs in
the recent emacs-w3m.  Probably they are due to the side effects
of the commits having done in months, I guess.  I'm afraid if
they might be deep rooted (should we be back to before having
migrated to git?, or just am I a culprit?).

1.
  In the emacs-w3m home page <http://emacs-w3m.namazu.org/>,
when I type <S-return> (`w3m-view-this-url-new-session') on
the name link `Features', the new tab appears and it shows
the Features section of the page.  That's ok.  However, if I
switch the tab to the original one, I can see the Features
section shown also there.  But what the original tab displays
should not be changed of course.

2.
  Clicking mouse-1, mouse-2, or C-mouse-wheel, etc. on a tab
causes this error (it happens regardless of the number of tabs):

Debugger entered--Lisp error: (error "Attempt to display deleted buffer")
  set-window-buffer(nil #<killed buffer>)
  switch-to-buffer(#<killed buffer>)
  w3m-tab-click-mouse-function((mouse-1...) #<killed buffer>)
  [...]

3.
  `M-n' (`w3m-copy-buffer') creates a new tab that is a copy of
the original.  However, the new tab is not selected.
  In addition, the place where the new tab appears does not get
always the leftmost of the tabs as the case may be.  This seems
to happen after creating a copy of a tab and further creating
a new tab by `G' (`w3m-goto-url-new-session'), etc.  In that case
`C-c C-p' (`w3m-previous-buffer') and `C-c C-n' (`w3m-next-buffer')
do not work correctly either.

Regards,
================================================================

System Info to help track down your bug:
---------------------------------------
emacs-w3m-git-revision
 => "a315e88f"
emacs-w3m-version
 => "1.4.632"
emacs-version
 => "GNU Emacs 27.0.50 (build 1, x86_64-pc-cygwin, GTK+ Version 3.22.28)\n of 2019-05-22"
mule-version
 => "6.0 (HANACHIRUSATO)"
system-type
 => cygwin
(featurep 'gtk)
 => t
w3m-version
 => "w3m/0.5.3+git20190421"
w3m-type
 => w3m-m17n
w3m-compile-options
 => ("lang=ja" "m17n" "image" "color" "ansi-color" "mouse" "menu" "cookie" "ssl" "ssl-verify" "external-uri-loader" "w3mmailer" "nntp" "ipv6" "alarm" "mark")
w3m-language
 => nil
w3m-command-arguments
 => nil
w3m-command-arguments-alist
 => nil
w3m-command-environment
 => (("LC_ALL" . "C"))
w3m-input-coding-system
 => utf-8
w3m-output-coding-system
 => utf-8
w3m-use-mule-ucs
 => nil