Rename modifier_state_changed to notify_modifiers

notify_modifiers will now synchronise Weston's internal state with the
XKB state, and send a modifier event if necessary.  This eliminates the
need for update_modifier_state to have a return value at all.

Signed-off-by: Daniel Stone <daniel@fooishbar.org>
diff --git a/src/compositor.h b/src/compositor.h
index 6e981f2..14420c5 100644
--- a/src/compositor.h
+++ b/src/compositor.h
@@ -511,6 +511,8 @@
 notify_key(struct wl_seat *seat, uint32_t time, uint32_t key,
 	   enum wl_keyboard_key_state state,
 	   enum weston_key_state_update update_state);
+void
+notify_modifiers(struct wl_seat *seat, uint32_t serial);
 
 void
 notify_pointer_focus(struct wl_seat *seat, struct weston_output *output,