Implement the relative pointer protocol

A wp_relative_pointer object is an extension to the wl_pointer interface
only used for emitting relative pointer events. It will only emit events
when the parent pointer has focus.

To get a relative pointer object, use the get_relative_pointer request
of the global wp_relative_pointer_manager object.

The relative pointer protocol is currently an unstable protocol, so
unstable protocol naming conventions has been applied.

Signed-off-by: Jonas Ådahl <jadahl@gmail.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
diff --git a/libweston/compositor.c b/libweston/compositor.c
index 4a0bfef..eb75c5f 100644
--- a/libweston/compositor.c
+++ b/libweston/compositor.c
@@ -4703,6 +4703,9 @@
 			      ec, bind_presentation))
 		goto fail;
 
+	if (weston_input_init(ec) != 0)
+		goto fail;
+
 	wl_list_init(&ec->view_list);
 	wl_list_init(&ec->plane_list);
 	wl_list_init(&ec->layer_list);