when one connection had done FLUSH TABLES WITH READ LOCK, some updates, and then COMMIT,
it was accepted but my_error() was called and so, while client got no error, error was logged in binlog.
We now don't call my_error() in this case; we assume the connection know what it does.
This problem was specific to 4.0.21. The change is needed to make replication work with existing versions of innobackup.
sql/lock.cc:
If a connection has done FLUSH TABLES WITH READ LOCK and now is doing COMMIT, don't give error
(applies only if it's the same connection; others' COMMITs are still blocked).
