Fix assorted compiler warnings.

sql/handler.cc:
  Initialize the "comment" member of the structure.
sql/sql_base.cc:
  Compile out unused function.
sql/sql_update.cc:
  Remove unused variable.
sql/sys_vars.cc:
  Use correct format specifier.

sql/handler.cc

@@ -46,7 +46,8 @@ static handlerton *installed_htons[128];
 
 #define BITMAP_STACKBUF_SIZE (128/8)
 
-KEY_CREATE_INFO default_key_create_info= { HA_KEY_ALG_UNDEF, 0, {NullS,0} };
+KEY_CREATE_INFO default_key_create_info=
+  { HA_KEY_ALG_UNDEF, 0, {NullS, 0}, {NullS, 0} };
 
 /* number of entries in handlertons[] */
 ulong total_ha= 0;

sql/sql_base.cc

@@ -729,6 +729,7 @@ TABLE_SHARE *get_cached_table_share(const char *db, const char *table_name)
 }  
 
 
+#ifdef DISABLED_UNTIL_GRL_IS_MADE_PART_OF_MDL
 /**
    @brief Mark table share as having one more user (increase its reference
           count).
@@ -746,6 +747,7 @@ static void reference_table_share(TABLE_SHARE *share)
                      (ulong) share, share->ref_count));
   DBUG_VOID_RETURN;
 }
+#endif
 
 
 /*

sql/sql_update.cc

@@ -206,7 +206,6 @@ int mysql_update(THD *thd,
   ulonglong     id;
   List<Item> all_fields;
   THD::killed_state killed_status= THD::NOT_KILLED;
-  MDL_ticket *start_of_statement_svp= thd->mdl_context.mdl_savepoint();
   DBUG_ENTER("mysql_update");
 
   if (open_tables(thd, &table_list, &table_count, 0))
@@ -956,7 +955,6 @@ int mysql_multi_update_prepare(THD *thd)
   uint  table_count= lex->table_count;
   const bool using_lock_tables= thd->locked_tables_mode != LTM_NONE;
   bool original_multiupdate= (thd->lex->sql_command == SQLCOM_UPDATE_MULTI);
-  MDL_ticket *start_of_statement_svp= thd->mdl_context.mdl_savepoint();
   DBUG_ENTER("mysql_multi_update_prepare");
 
   /* following need for prepared statements, to run next time multi-update */

sql/sys_vars.cc

@@ -2803,7 +2803,7 @@ static Sys_var_charptr Sys_slave_load_tmpdir(
 static bool fix_slave_net_timeout(sys_var *self, THD *thd, enum_var_type type)
 {
   mysql_mutex_lock(&LOCK_active_mi);
-  DBUG_PRINT("info", ("slave_net_timeout=%lu mi->heartbeat_period=%.3f",
+  DBUG_PRINT("info", ("slave_net_timeout=%u mi->heartbeat_period=%.3f",
                      slave_net_timeout,
                      (active_mi? active_mi->heartbeat_period : 0.0)));
   if (active_mi && slave_net_timeout < active_mi->heartbeat_period)