git.el: Try to reuse an existing buffer when running git-status.

By default, running git-status again will now reuse an existing buffer
that displays the same directory. The old behavior of always creating
a new buffer can be obtained by customizing the git-reuse-status-buffer
option.

Signed-off-by: Alexandre Julliard <julliard@winehq.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

contrib/emacs/git.el

@@ -83,6 +83,12 @@ then to `add-log-mailing-address' and then to `user-mail-address'."
   :group 'git
   :type 'boolean)
 
+(defcustom git-reuse-status-buffer t
+  "Whether `git-status' should try to reuse an existing buffer
+if there is already one that displays the same directory."
+  :group 'git
+  :type 'boolean)
+
 (defcustom git-per-dir-ignore-file ".gitignore"
   "Name of the per-directory ignore file."
   :group 'git
@@ -1003,12 +1009,28 @@ Commands:
   (set (make-local-variable 'list-buffers-directory) default-directory)
   (run-hooks 'git-status-mode-hook)))
 
+(defun git-find-status-buffer (dir)
+  "Find the git status buffer handling a specified directory."
+  (let ((list (buffer-list))
+        (fulldir (expand-file-name dir))
+        found)
+    (while (and list (not found))
+      (let ((buffer (car list)))
+        (with-current-buffer buffer
+          (when (and list-buffers-directory
+                     (string-equal fulldir (expand-file-name list-buffers-directory))
+                     (string-match "\\*git-status\\*$" (buffer-name buffer)))
+            (setq found buffer))))
+      (setq list (cdr list)))
+    found))
+
 (defun git-status (dir)
   "Entry point into git-status mode."
   (interactive "DSelect directory: ")
   (setq dir (git-get-top-dir dir))
   (if (file-directory-p (concat (file-name-as-directory dir) ".git"))
-      (let ((buffer (create-file-buffer (expand-file-name "*git-status*" dir))))
+      (let ((buffer (or (and git-reuse-status-buffer (git-find-status-buffer dir))
+                        (create-file-buffer (expand-file-name "*git-status*" dir)))))
         (switch-to-buffer buffer)
         (cd dir)
         (git-status-mode)