Adds support in src/core for tracking override redirect windows.

The metacity core is now directly aware of override redirect windows.
- They get MetaWindows like normal windows, so mutter no longer need to special
  case them. The net wm types applicable to override redirects are also
  recognised.
- The original positioning/stacking semantics of metacity with respect to OR
  windows are maintained, but now it's easier to synchronize the stacking
  between the core and mutter.
- mutter no longer needs to manualy track UnmapNotify, MapNotify,
  ReparentNotify, CreateNotify and DestroyNotify events; instead map, unmap,
  add and remove events can now be consistently delivered via the
  MetaCompositor callbacks.

src/core/session.c

@@ -698,6 +698,20 @@ window_type_to_string (MetaWindowType type)
       return "splashscreen";
     case META_WINDOW_UTILITY:
       return "utility";
+    case META_WINDOW_DROPDOWN_MENU:
+      return "dropdown_menu";
+    case META_WINDOW_POPUP_MENU:
+      return "popup_menu";
+    case META_WINDOW_TOOLTIP:
+      return "tooltip";
+    case META_WINDOW_NOTIFICATION:
+      return "notification";
+    case META_WINDOW_COMBO:
+      return "combo";
+    case META_WINDOW_DND:
+      return "dnd";
+    case META_WINDOW_OVERRIDE_OTHER:
+      return "override_redirect";
     }
 
   return "";