In `debug' don't try using window on inaccessible frame (Bug#17170).

* emacs-lisp/debug.el (debug): Don't try using "previous"
window when its not live or on an invisible frame (Bug#17170).

lisp/ChangeLog

+2015-03-22  Martin Rudalics  <rudalics@gmx.at>
+
+	* emacs-lisp/debug.el (debug): Don't try using "previous" window
+	when its not live or on an invisible frame (Bug#17170).
+
 2015-03-21  Mario Lang  <mlang@delysid.org>
 
 	* emacs-lisp/tabulated-list.el (tabulated-list-print): Only call

lisp/emacs-lisp/debug.el

@@ -193,8 +193,10 @@ first will be printed into the backtrace buffer."
 	       debugger-buffer
 	       `((display-buffer-reuse-window
 		  display-buffer-in-previous-window)
-		  . (,(when debugger-previous-window
-			`(previous-window . ,debugger-previous-window)))))
+		 . (,(when (and (window-live-p debugger-previous-window)
+				(frame-visible-p
+				 (window-frame debugger-previous-window)))
+		       `(previous-window . ,debugger-previous-window)))))
 	      (setq debugger-window (selected-window))
 	      (if (eq debugger-previous-window debugger-window)
 		  (when debugger-jumping-flag