DO NOT COPY THIS CODE TO 4.0. The bugfix is better in 4.0,
but here in 3.23 we don't want to add a new error code so
we just use ER_EMPTY_QUERY. Bug was:
"If a query was ignored on the slave (because of
@code{replicate-ignore-table} and other similar rules), the slave
still checked if the query got the same error code (0, no error) as on
the master. So if the master had an error on the query (for example,
``Duplicate entry'' in a multiple-row insert), then the slave stopped
and warned that the error codes didn't match. (Bug #797)"


sql/slave.cc:
  Ignore ER_EMPTY_QUERY as it is also a marker for "query was ignored because 
  of replicate-*-table rules".
sql/sql_parse.cc:
  In a slave thread, mark an ignored query (because of replicate-*-table rules)
  as empty. The caller, exec_event(), will understand this error code as "ignorable
  query, don't compare the error codes on master and slave".