bug#6762: 23.2; Eshell bug in detecting read-only file (patch included)

[Leo]

I have diff-default-read-only set to t and this prevents eshell from
writing to diff files i.e.

  ESHELL$ git diff x..y > file.diff

fails due to its use of buffer-read-only, which doesn't necessary
reflects the read-only state of a file.

The following patch tries to fix this.

Leo

commit b1dc6a427e43470981d4700b0c98aa21ecb03052
Author: sdl.web@gmail.com
Date:   Sat May 1 17:50:21 2010 +0100

    Better detection of read-only file in eshell-get-target

        Modified lisp/eshell/esh-io.el
diff --git a/lisp/eshell/esh-io.el b/lisp/eshell/esh-io.el
index 1bcfe2b..3aa785c 100644
--- a/lisp/eshell/esh-io.el
+++ b/lisp/eshell/esh-io.el
@@ -343,8 +343,9 @@ it defaults to `insert'."
        (let* ((exists (get-file-buffer target))
               (buf (find-file-noselect target t)))
          (with-current-buffer buf
-           (if buffer-read-only
+           (if buffer-file-read-only
                (error "Cannot write to read-only file `%s'" target))
+           (setq buffer-read-only nil)
            (set (make-local-variable 'eshell-output-file-buffer)
                 (if (eq exists buf) 0 t))
            (cond ((eq mode 'overwrite)