(rmail-get-new-mail): Fix return value to match doc.

lisp/mail/rmail.el

@@ -916,6 +916,7 @@ It returns t if it got any new messages."
   (let ((all-files (if file-name (list file-name)
 		     rmail-inbox-list)))
     (unwind-protect
+	(let (found)
 	  (while all-files
 	    (let ((opoint (point))
 		  (new-messages 0)
@@ -998,8 +999,7 @@ It returns t if it got any new messages."
 	      (if (= new-messages 0)
 		  (progn (goto-char opoint)
 			 (if (or file-name rmail-inbox-list)
-			   (message "(No new mail has arrived)"))
-		       nil)
+			     (message "(No new mail has arrived)")))
 		(if (rmail-summary-exists)
 		    (rmail-select-summary
 		     (rmail-update-summary)))
@@ -1009,7 +1009,8 @@ It returns t if it got any new messages."
 		;; unless we have other unseen messages before it.
 		(rmail-show-message (rmail-first-unseen-message))
 		(run-hooks 'rmail-after-get-new-mail-hook)
-	      t)))
+		(setq found t))))
+	  found)
       ;; Don't leave the buffer screwed up if we get a disk-full error.
       (rmail-show-message))))