Scripts/Wintergrasp: enable script and add it to spell_script_names

sql/updates/world/2012_08_23_00_world_wintergrasp_spell_script_names.sql

@@ -0,0 +1,3 @@
+DELETE FROM `spell_script_names` WHERE `spell_id` = 54640;
+INSERT INTO `spell_script_names` (`spell_id`,`ScriptName`) VALUES
+(54640, 'spell_wintergrasp_defender_teleport');

src/server/scripts/Northrend/wintergrasp.cpp

@@ -585,4 +585,5 @@ void AddSC_wintergrasp()
     new spell_wintergrasp_force_building();
     new spell_wintergrasp_grab_passenger();
     new achievement_wg_didnt_stand_a_chance();
+    new spell_wintergrasp_defender_teleport();
 }