Feature: Wintype-based focus exclusion

- Add "focus" to the wintypes settings in compton.conf, to mark windows
  of certain window types to be always focused. Replaces the ugly
  is_normal_win().

- Add a ON/OFF/UNSET switch_t type, but it's unused currently.

- Mark client_win if the window client detection hasn't been performed
  when we detect WM_STATE's presence in ev_property_notify(), for
  performance.

compton.sample.conf

@@ -47,5 +47,5 @@ focus-exclude = [ ];
 # Window type settings
 wintypes:
 {
-  tooltip = { fade = true; shadow = false; opacity = 0.75; };
+  tooltip = { fade = true; shadow = false; opacity = 0.75; focus = true; };
 };