bug#34939: Some minibuffer behaviour is annoying

[Juri Linkov <juri@linkov.net>]

>> (1) when I press backspace and the prompt is empty, minibuffer tells me
>> "Text is read-only". You. Don't. Say.
>
> Messages in the echo area should not conceal the minibuffer.  Period.
>
> There is a special function minibuffer-message for this purpose:

There is another place where messages conceal the minibuffer:
running a version-control command that asks for a branch name
and typing TAB for completion runs a command to fetch branch names.
Its output conceals the minibuffer when vc-command-messages is non-nil.
Here is a fix:

diff --git a/lisp/vc/vc-dispatcher.el b/lisp/vc/vc-dispatcher.el
index edbb83f3df..c4b327a3f0 100644
--- a/lisp/vc/vc-dispatcher.el
+++ b/lisp/vc/vc-dispatcher.el
@@ -324,7 +324,8 @@ vc-do-command
 		       (apply 'start-file-process command (current-buffer)
                               command squeezed))))
 		(when vc-command-messages
-		  (message "Running in background: %s" full-command))
+		  (let ((inhibit-message (eq (selected-window) (active-minibuffer-window))))
+		    (message "Running in background: %s" full-command)))
                 ;; Get rid of the default message insertion, in case we don't
                 ;; set a sentinel explicitly.
 		(set-process-sentinel proc #'ignore)
@@ -332,11 +333,13 @@ vc-do-command
 		(setq status proc)
 		(when vc-command-messages
 		  (vc-run-delayed
-		    (let ((message-truncate-lines t))
+		    (let ((message-truncate-lines t)
+			  (inhibit-message (eq (selected-window) (active-minibuffer-window))))
 		      (message "Done in background: %s" full-command)))))
 	    ;; Run synchronously
 	    (when vc-command-messages
-	      (message "Running in foreground: %s" full-command))
+	      (let ((inhibit-message (eq (selected-window) (active-minibuffer-window))))
+		(message "Running in foreground: %s" full-command)))
 	    (let ((buffer-undo-list t))
 	      (setq status (apply 'process-file command nil t nil squeezed)))
 	    (when (and (not (eq t okstatus))
@@ -350,7 +353,8 @@ vc-do-command
 		     (if (integerp status) (format "status %d" status) status)
 		     full-command))
 	    (when vc-command-messages
-	      (message "Done (status=%d): %s" status full-command))))
+	      (let ((inhibit-message (eq (selected-window) (active-minibuffer-window))))
+		(message "Done (status=%d): %s" status full-command)))))
 	(vc-run-delayed
 	  (run-hook-with-args 'vc-post-command-functions
 			      command file-or-list flags))