Fix some minor shell.el oddness related to usage of error and message

* lisp/shell.el (shell-directory-tracker): Output error as a message
rather than just returning it as a string.
(shell-process-pushd): Remove useless use of message.

lisp/ChangeLog

@@ -1,5 +1,9 @@
 2013-09-12  Glenn Morris  <rgm@gnu.org>
 
+	* shell.el (shell-directory-tracker): Output error as a message
+	rather than just returning it as a string.
+	(shell-process-pushd): Remove useless use of message.
+
 	* dframe.el (dframe-timer-fn):
 	* files.el (dir-locals-read-from-file):
 	* mpc.el (mpc--status-timer-run, mpc--status-idle-timer-run)

lisp/shell.el

@@ -791,7 +791,7 @@ and `shell-pushd-dunique' control the behavior of the relevant command.
 Environment variables are expanded, see function `substitute-in-file-name'."
   (if shell-dirtrackp
       ;; We fail gracefully if we think the command will fail in the shell.
-      (condition-case nil
+      (with-demoted-errors "Couldn't cd: %s"
 	  (let ((start (progn (string-match
 			       (concat "^" shell-command-separator-regexp)
 			       str) ; skip whitespace
@@ -824,8 +824,7 @@ Environment variables are expanded, see function `substitute-in-file-name'."
 	      (setq start (progn (string-match shell-command-separator-regexp
 					       str end)
 				 ;; skip again
-				 (match-end 0)))))
-	(error "Couldn't cd"))))
+				 (match-end 0))))))))
 
 (defun shell-unquote-argument (string)
   "Remove all kinds of shell quoting from STRING."
@@ -907,7 +906,7 @@ Environment variables are expanded, see function `substitute-in-file-name'."
 	   (cond ((> num (length shell-dirstack))
 		  (message "Directory stack not that deep."))
 		 ((= num 0)
-		  (error (message "Couldn't cd")))
+		  (error "Couldn't cd"))
 		 (shell-pushd-dextract
 		  (let ((dir (nth (1- num) shell-dirstack)))
 		    (shell-process-popd arg)