Query_log_event::error_code

A query can perform completely having the local var error of mysql_$query
zero, where $query in insert, update, delete, load,
and be  binlogged with error_code e.g KILLED_QUERY while there is no
reason do to so.
That can happen because Query_log_event consults thd->killed flag to
evaluate error_code.

Fixed with implementing a scheme suggested and partly implemented at
time of bug@22725 work-on. error_status is cached immediatly after the
control leaves the main rows-loop and that instance always corresponds
to `error' the local of mysql_$query functions. The cached value
is passed to Query_log_event constructor, not the default thd->killed
which can be changed in between of the caching and the constructing.