buff-menu: Add command to unmark all buffers

Bind 'U' in buff-menu, bs and electric-buff-menu to commands
to unmark all buffers (Bug#24880).
* lisp/emacs-lisp/tabulated-list.el (tabulated-list-header-overlay-p):
New predicate; return non-nil if tabulated-list has a fake header.
* lisp/buff-menu.el (Buffer-menu-unmark-all-buffers):
New command; remove all flags that use a particular mark from all the lines.
Bind it to 'M-DEL'.
(Buffer-menu-unmark-all):
New command; remove all flags from all the lines.  Bind it to 'U'.
(Buffer-menu-marker-char, Buffer-menu-del-char): New variables.
(Buffer-menu-delete, Buffer-menu-mark): Use them.
(Buffer-menu-mode-map): Update menus.
(Buffer-menu-mode): Update mode doc.
* lisp/bs.el (bs-unmark-all, bs-unmark-previous): New commands.
(bs-mode-map): Bind them to 'U' and '<backspace>' respectively.
(bs-mode): Update mode doc.
* lisp/ebuff-menu.el (electric-buffer-menu-mode-map):
Bind Buffer-menu-unmark-all to 'U' and Buffer-menu-unmark-all-buffers
to 'M-DEL'.
(bs--down, bs-down, bs--up, bs-up, bs-unmark-current, bs-mark-current):
Use point instead of cursor in doc string.
(electric-buffer-list): Update mode doc.
* doc/emacs/buffers.texi (Several Buffers): Mention Buffer-menu-unmark-all
and Buffer-menu-unmark-all-buffers.
; * etc/NEWS: Add an entry per each new feature.

1 files changed, 18 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 619d56ba7b7..02e93e4f9fb 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -283,6 +283,24 @@ the file's actual content before prompting the user.
 
 * Changes in Specialized Modes and Packages in Emacs 26.1
 
+** Electric-Buffer-menu
+
++++
+*** Key 'U' is bound to 'Buffer-menu-unmark-all' and key 'M-DEL' is
+bound to 'Buffer-menu-unmark-all-buffers'.
+
+** bs
+
+---
+*** Two new commands 'bs-unmark-all', bound to 'U', and
+'bs-unmark-previous', bound to <backspace>.
+
+** Buffer-menu
+
++++
+*** Two new commands 'Buffer-menu-unmark-all', bound to 'U' and
+'Buffer-menu-unmark-all-buffers', bound to 'M-DEL'.
+
 ** Ibuffer
 
 ---