wayland/pointer-gestures: Send error on protocol version mismatch

When a client binds an incompatible version, we should terminate it.
This check should only be there for the unstable version, as once it is
declared stable and renamed, future versions will be backward compatible.

https://bugzilla.gnome.org/show_bug.cgi?id=753855

src/wayland/meta-wayland-pointer-gestures.c

@@ -67,6 +67,15 @@ bind_pointer_gestures (struct wl_client *client,
   struct wl_resource *resource;
 
   resource = wl_resource_create (client, &_wl_pointer_gestures_interface, version, id);
+
+  if (version != META__WL_POINTER_GESTURES_VERSION)
+    {
+      wl_resource_post_error (resource,
+                              _WL_POINTER_GESTURES_ERROR_VERSION_MISMATCH,
+                              "The client bound a non-supported version");
+      return;
+    }
+
   wl_resource_set_implementation (resource, &pointer_gestures_interface,
                                   NULL, NULL);
 }
@@ -76,6 +85,6 @@ meta_wayland_pointer_gestures_init (MetaWaylandCompositor *compositor)
 {
   wl_global_create (compositor->wayland_display,
                     &_wl_pointer_gestures_interface,
-                    META_WL_POINTER_GESTURES_VERSION,
+                    META__WL_POINTER_GESTURES_VERSION,
                     NULL, bind_pointer_gestures);
 }

src/wayland/meta-wayland-versions.h

@@ -44,6 +44,6 @@
 #define META_XSERVER_VERSION                1
 #define META_GTK_SHELL_VERSION              2
 #define META_WL_SUBCOMPOSITOR_VERSION       1
-#define META_WL_POINTER_GESTURES_VERSION    1
+#define META__WL_POINTER_GESTURES_VERSION   1
 
 #endif

src/wayland/protocol/pointer-gestures.xml

@@ -16,6 +16,10 @@
       name and the version will be reset to 1.
     </description>
 
+    <enum name="error">
+      <entry name="version_mismatch" value="0"/>
+    </enum>
+
     <request name="get_swipe_gesture">
       <description summary="get swipe gesture">
 	Create a swipe gesture object. See the