InnoDB is limited to row-logging when transaction isolation level is
READ COMMITTED or READ UNCOMMITTED. This limitation is enforced by
a check within ha_innobase::external_lock().
InnoDB also expects number of "successful external locks" to match
number of "external unlocks", which is controlled by the assertion
in subject.
However "unlock" was called even after failing "lock" for high-level
indexes.
Fixed by calling "unlock" only after "successful lock".
ignore FK-prelocked tables when looking for write-prelocked tables
with auto-increment to complain about "Statement is unsafe because
it invokes a trigger or a stored function that inserts into an
AUTO_INCREMENT column"
