For UPDATEs involving a single table, the server call to handler::direct_update_rows() is used to correctly set the count for the number of updated rows in the UPDATE statement.
However, for UPDATEs involving multi-tables, the server does not call handler::direct_update_rows(). This patch adds support to correctly report the number of updated rows to the client by setting
multi_update::updated and multi_update::found in handler::rnd_end().
