Fix for bug #30200: mysqlbinlog.test: connection_id() not restored under ps-protocol

Problem: thd->thread_specific_used flag is not set executing a statement
containig connection_id() function using PS protocol, that leads to 
improper binlog event creation.

Fix: set the flag in the Item_func_connection_id::fix_fields().

sql/item_create.cc

@@ -72,7 +72,6 @@ Item *create_func_connection_id(void)
 {
   THD *thd= current_thd;
   thd->lex->safe_to_cache_query= 0;
-  thd->thread_specific_used= TRUE;
   return new Item_func_connection_id();
 }
 

sql/item_func.cc

@@ -649,6 +649,7 @@ bool Item_func_connection_id::fix_fields(THD *thd, Item **ref)
 {
   if (Item_int_func::fix_fields(thd, ref))
     return TRUE;
+  thd->thread_specific_used= TRUE;
   value= thd->variables.pseudo_thread_id;
   return FALSE;
 }

sql/sql_parse.cc

@@ -5847,6 +5847,7 @@ void mysql_reset_thd_for_next_command(THD *thd)
                           SERVER_QUERY_NO_GOOD_INDEX_USED);
   DBUG_ASSERT(thd->security_ctx== &thd->main_security_ctx);
   thd->tmp_table_used= 0;
+  thd->thread_specific_used= FALSE;
   if (!thd->in_sub_stmt)
   {
     if (opt_bin_log)