Improvement: Change in client window lookup & wintype detection

- Revert to WM_STATE for client window lookup, as WM_CLASS is
  unreliable, either, but set the client window of an override-redirect
  window to itself.

- Conform to EWMH to make assumptions about window types when
  _NET_WM_WINDOW_TYPE is not available.

- Remove determine_wintype() and completely rely on client window for
  window type detection.

src/compton.h

@@ -631,8 +631,7 @@ solid_picture(Display *dpy, Bool argb, double a,
 
 static inline bool is_normal_win(const win *w) {
   return (WINTYPE_NORMAL == w->window_type
-      || WINTYPE_UTILITY == w->window_type
-      || WINTYPE_UNKNOWN == w->window_type);
+      || WINTYPE_UTILITY == w->window_type);
 }
 
 /**
@@ -761,9 +760,6 @@ repair_win(Display *dpy, win *w);
 static wintype
 get_wintype_prop(Display * dpy, Window w);
 
-static wintype
-determine_wintype(Display *dpy, Window w);
-
 static void
 map_win(Display *dpy, Window id,
         unsigned long sequence, Bool fade,