Issue an error message to the error log when
trx->dict_operation_lock_mode == RW_X_LATCH in
srv_suspend_mysql_thread(). Transactions that modify InnoDB
data dictionary tables must be free of lock waits, because they
must be holding the data dictionary latch in exclusive mode.
The transactions must not be accessing any other tables other than
the data dictionary tables.

The handling of RW_X_LATCH was accidentally added in the InnoDB Plugin,
as a wrong fix of an assertion failure. (Fast index creation was accessing
both data dictionary tables and user tables in the same transaction.)