allow recovery UI to ignore certain keypresses

Change-Id: Id182bb95ffcc475c5acabb29b413e422302ae7f2
diff --git a/ui.h b/ui.h
index 750b993..0d3b7bb 100644
--- a/ui.h
+++ b/ui.h
@@ -73,7 +73,7 @@
     // Return value indicates whether an immediate operation should be
     // triggered (toggling the display, rebooting the device), or if
     // the key should be enqueued for use by the main thread.
-    enum KeyAction { ENQUEUE, TOGGLE, REBOOT };
+    enum KeyAction { ENQUEUE, TOGGLE, REBOOT, IGNORE };
     virtual KeyAction CheckKey(int key);
 
     // --- menu display ---