Simplify Gnus buffer liveness checking and killing

* lisp/gnus/gnus-agent.el (gnus-agent-synchronize-group-flags):
Fix indentation.
* lisp/gnus/gnus-util.el (gnus-buffer-exists-p): Define as obsolete
alias of gnus-buffer-live-p.
(gnus-buffer-live-p): If the given argument is or names a live
buffer, return the corresponding buffer object instead of a boolean.
* lisp/gnus/gnus-win.el (gnus-delete-windows-in-gnusey-frames)
(gnus-remove-some-windows): Simplify.
* lisp/gnus/gnus.el (gnus-prune-buffers): Redefine as alias of
gnus-buffers.
(gnus-kill-buffer, gnus-buffers, gnus-group-find-parameter):
* lisp/gnus/gnus-art.el (gnus-kill-sticky-article-buffers)
(gnus-request-article-this-buffer):
* lisp/gnus/gnus-bcklg.el (gnus-backlog-shutdown):
* lisp/gnus/gnus-cus.el (gnus-group-customize)
(gnus-agent-customize-category):
* lisp/gnus/gnus-draft.el (gnus-draft-edit-message):
* lisp/gnus/gnus-group.el (gnus-group-set-mode-line)
(gnus--abort-on-unsaved-message-buffers, gnus-group-compact-group):
* lisp/gnus/gnus-msg.el (gnus-inews-add-send-actions)
(gnus-summary-supersede-article, gnus-copy-article-buffer):
* lisp/gnus/gnus-score.el (gnus-score-edit-current-scores)
(gnus-score-edit-file):
* lisp/gnus/gnus-spec.el (gnus-update-format-specifications):
* lisp/gnus/gnus-srvr.el (gnus-server-compact-server):
* lisp/gnus/gnus-start.el (gnus-clear-system, gnus-dribble-enter)
(gnus-dribble-save, gnus-dribble-clear, gnus-save-newsrc-file):
* lisp/gnus/gnus-sum.el (gnus-summary-setup-buffer)
(gnus-update-summary-mark-positions, gnus-summary-exit)
(gnus-deaden-summary, gnus-kill-or-deaden-summary)
(gnus-summary-next-group):
* lisp/gnus/gnus-win.el (gnus-configure-frame):
* lisp/gnus/mail-source.el (mail-source-movemail):
* lisp/gnus/message.el (message-with-reply-buffer)
(message-with-reply, message-send-and-exit)
(message-send-mail-with-sendmail, message-pop-to-buffer)
(message-do-send-housekeeping, message-forward-make-body-plain)
(message-forward-make-body-mml):
* lisp/gnus/mm-decode.el (mm-display-external, mm-remove-part):
* lisp/gnus/nnbabyl.el (nnbabyl-server-opened)
(nnbabyl-possibly-change-newsgroup, nnbabyl-read-mbox)
(nnbabyl-check-mbox):
* lisp/gnus/nndiary.el (nndiary-save-nov):
* lisp/gnus/nndoc.el (nndoc-close-group)
(nndoc-possibly-change-buffer):
* lisp/gnus/nnfolder.el (nnfolder-close-group, nnfolder-save-nov):
* lisp/gnus/nnimap.el (nnimap-make-process-buffer, nnimap-keepalive)
(nnimap-find-connection):
* lisp/gnus/nnmail.el (nnmail-cache-open, nnmail-cache-close):
* lisp/gnus/nnmbox.el (nnmbox-close-server, nnmbox-server-opened)
(nnmbox-possibly-change-newsgroup, nnmbox-read-mbox):
* lisp/gnus/nnml.el (nnml-save-incremental-nov, nnml-open-nov)
(nnml-save-nov):
* lisp/gnus/nnoo.el (nnoo-server-opened):
* lisp/gnus/nntp.el (nntp-kill-buffer, nntp-make-process-buffer)
(nntp-open-connection, nntp-async-trigger):
* lisp/net/mairix.el (mairix-gnus-fetch-field): Simplify buffer
liveness checking and killing, replacing buffer-name with
buffer-live-p and gnus-buffer-exists-p with gnus-buffer-live-p or
equivalent where applicable.

lisp/gnus/gnus-sum.el

@@ -3519,8 +3519,7 @@ Returns non-nil if the setup was successful."
 	(dead-name (concat "*Dead Summary "
 			   (gnus-group-decoded-name group) "*")))
     ;; If a dead summary buffer exists, we kill it.
-    (when (gnus-buffer-live-p dead-name)
-      (gnus-kill-buffer dead-name))
+    (gnus-kill-buffer dead-name)
     (if (get-buffer buffer)
 	(progn
 	  (set-buffer buffer)
@@ -3622,7 +3621,7 @@ buffer that was in action when the last article was fetched."
 (defun gnus-update-summary-mark-positions ()
   "Compute where the summary marks are to go."
   (save-excursion
-    (when (gnus-buffer-exists-p gnus-summary-buffer)
+    (when (gnus-buffer-live-p gnus-summary-buffer)
       (set-buffer gnus-summary-buffer))
     (let ((spec gnus-summary-line-format-spec)
 	  pos)
@@ -7326,7 +7325,7 @@ If FORCE (the prefix), also save the .newsrc file(s)."
       (gnus-summary-update-info))
     (gnus-close-group group)
     ;; Make sure where we were, and go to next newsgroup.
-    (when (buffer-live-p (get-buffer gnus-group-buffer))
+    (when (gnus-buffer-live-p gnus-group-buffer)
       (set-buffer gnus-group-buffer))
     (unless quit-config
       (gnus-group-jump-to-group group))
@@ -7501,8 +7500,7 @@ The state which existed when entering the ephemeral is reset."
 (defun gnus-deaden-summary ()
   "Make the current summary buffer into a dead summary buffer."
   ;; Kill any previous dead summary buffer.
-  (when (and gnus-dead-summary
-	     (buffer-name gnus-dead-summary))
+  (when (buffer-live-p gnus-dead-summary)
     (with-current-buffer gnus-dead-summary
       (when gnus-dead-summary-mode
 	(kill-buffer (current-buffer)))))
@@ -7520,7 +7518,7 @@ The state which existed when entering the ephemeral is reset."
 (defun gnus-kill-or-deaden-summary (buffer)
   "Kill or deaden the summary BUFFER."
   (save-excursion
-    (when (and (buffer-name buffer)
+    (when (and (buffer-live-p buffer)
 	       (not gnus-single-article-buffer))
       (with-current-buffer buffer
 	(gnus-kill-buffer gnus-article-buffer)
@@ -7529,12 +7527,12 @@ The state which existed when entering the ephemeral is reset."
      ;; Kill the buffer.
      (gnus-kill-summary-on-exit
       (when (and gnus-use-trees
-		 (gnus-buffer-exists-p buffer))
+                 (gnus-buffer-live-p buffer))
 	(with-current-buffer buffer
 	  (gnus-tree-close)))
       (gnus-kill-buffer buffer))
      ;; Deaden the buffer.
-     ((gnus-buffer-exists-p buffer)
+     ((gnus-buffer-live-p buffer)
       (with-current-buffer buffer
 	(gnus-deaden-summary))))))
 
@@ -7605,7 +7603,7 @@ previous group instead."
 		       (and unreads (not (zerop unreads))))
  		   (gnus-summary-read-group
  		    target-group nil no-article
- 		    (and (buffer-name current-buffer) current-buffer)
+                    (and (buffer-live-p current-buffer) current-buffer)
  		    nil backward))
 	      (setq entered t)
 	    (setq current-group target-group