bug#18096: 24.3.92; async shell command and a busy buffer leads to error

[Juri Linkov]

> --- a/lisp/simple.el
> +++ b/lisp/simple.el
> @@ -2904,7 +2904,8 @@ the use of a shell (with its need to quote arguments)."
>                     (error "Shell command in progress")))
>                  ((eq async-shell-command-buffer 'confirm-new-buffer)
>                   ;; If will create a new buffer, query first.
> -                 (if (yes-or-no-p "A command is running in the default 
> buffer.  Use a new buffer? ")
> +                 (if (and (stringp output-buffer)
> +                             (yes-or-no-p "A command is running in the 
> default buffer.  Use a new buffer? "))
>                       (setq buffer (generate-new-buffer
>                                     (or output-buffer "*Async Shell 
> Command*")))
>                     (error "Shell command in progress")))

This will ignore the user customization in `async-shell-command-buffer'
if the user want it to ask a question whether to create a new buffer.
More tolerating would be trying to get a new buffer name even when
the given argument is a buffer:

=== modified file 'lisp/simple.el'
--- lisp/simple.el      2014-07-08 08:27:45 +0000
+++ lisp/simple.el      2014-07-27 23:44:20 +0000
@@ -2986,12 +2986,14 @@ (defun shell-command (command &optional
                    ;; If will create a new buffer, query first.
                    (if (yes-or-no-p "A command is running in the default 
buffer.  Use a new buffer? ")
                        (setq buffer (generate-new-buffer
-                                     (or output-buffer "*Async Shell 
Command*")))
+                                     (or (and (bufferp output-buffer) 
(buffer-name output-buffer))
+                                         output-buffer "*Async Shell 
Command*")))
                      (error "Shell command in progress")))
                   ((eq async-shell-command-buffer 'new-buffer)
                    ;; It will create a new buffer.
                    (setq buffer (generate-new-buffer
-                                 (or output-buffer "*Async Shell Command*"))))
+                                 (or (and (bufferp output-buffer) (buffer-name 
output-buffer))
+                                     output-buffer "*Async Shell Command*"))))
                   ((eq async-shell-command-buffer 'confirm-rename-buffer)
                    ;; If will rename the buffer, query first.
                    (if (yes-or-no-p "A command is running in the default 
buffer.  Rename it? ")