debug_sync is now a service, available to dynamically loaded plugins.

new make target - abi_update

libservices/HOWTO:
  remove references to Makefile.am
  small tweaks

sql/sql_plugin.cc

@@ -1520,6 +1520,10 @@ int plugin_init(int *argc, char **argv, int flags)
       goto err;
   }
 
+  /* prepare debug_sync service */
+  DBUG_ASSERT(strcmp(list_of_services[5].name, "debug_sync_service") == 0);
+  list_of_services[5].service= *(void**)&debug_sync_C_callback_ptr;
+
   mysql_mutex_lock(&LOCK_plugin);
 
   initialized= 1;