Bug#12713 "Error in a stored function called from a SELECT doesn't

cause ROLLBACK of statement", part 1. Review fixes.

Do not send OK/EOF packets to the client until we reached the end of 
the current statement.
This is a consolidation, to keep the functionality that is shared by all 
SQL statements in one place in the server.
Currently this functionality includes:
- close_thread_tables()
- log_slow_statement().

After this patch and the subsequent patch for Bug#12713, it shall also include:
- ha_autocommit_or_rollback()
- net_end_statement()
- query_cache_end_of_result().

In future it may also include:
- mysql_reset_thd_for_next_command().

server-tools/instance-manager/mysql_connection.cc

@@ -257,7 +257,7 @@ int Mysql_connection::do_command()
       return 1;
     if (thread_registry->is_shutdown())
       return 1;
-    net_send_error(&net, net.last_errno);
+    net_send_error(&net, net.client_last_errno);
     net.error= 0;
     return 0;
   }