Put error output from M-! at the end of the error buffer

* lisp/simple.el (shell-command-on-region): Put the error output
at the end of the buffer instead of wherever point is (bug#7513).
This avoids interleaving error output.

lisp/simple.el

@@ -3944,15 +3944,14 @@ interactively, this is t."
     (when (and error-file (file-exists-p error-file))
       (if (< 0 (file-attribute-size (file-attributes error-file)))
 	  (with-current-buffer (get-buffer-create error-buffer)
-	    (let ((pos-from-end (- (point-max) (point))))
-	      (or (bobp)
-		  (insert "\f\n"))
-	      ;; Do no formatting while reading error file,
-	      ;; because that can run a shell command, and we
-	      ;; don't want that to cause an infinite recursion.
-	      (format-insert-file error-file nil)
-	      ;; Put point after the inserted errors.
-	      (goto-char (- (point-max) pos-from-end)))
+            (goto-char (point-max))
+            ;; Insert a separator if there's already text here.
+	    (unless (bobp)
+	      (insert "\f\n"))
+	    ;; Do no formatting while reading error file,
+	    ;; because that can run a shell command, and we
+	    ;; don't want that to cause an infinite recursion.
+	    (format-insert-file error-file nil)
 	    (and display-error-buffer
 		 (display-buffer (current-buffer)))))
       (delete-file error-file))