Improvement: --unredir-if-possible-exclude & --unredir-if-possible-delay

- Add --unredir-if-possible-exclude, to exclude certain windows when
  evaluating --unredir-if-possible. (#140)

- Add --unredir-if-possible-delay, to add some delay before
  unredirecting screen. (#138, #140)

- Code clean-up.

src/compton.h

@@ -324,6 +324,14 @@ ms_to_tv(int timeout) {
   };
 }
 
+/**
+ * Whether an event is DamageNotify.
+ */
+static inline bool
+isdamagenotify(session_t *ps, const XEvent *ev) {
+  return ps->damage_event + XDamageNotify == ev->type;
+}
+
 /**
  * Create a XTextProperty of a single string.
  */
@@ -1205,6 +1213,9 @@ timeout_get_poll_time(session_t *ps);
 static void
 timeout_clear(session_t *ps);
 
+static bool
+tmout_unredir_callback(session_t *ps, timeout_t *tmout);
+
 static bool
 mainloop(session_t *ps);