mysql-test/t/trigger.test:
  Replace all numeric error code with symbolic names.
  Left are --error 1 for system error, and --error 1100.  The
  symbolic constant for the latter is ER_TABLE_NOT_LOCKED, but using
  it triggers a bug in test driver due to name prefix collision with
  1099 ER_TABLE_NOT_LOCKED_FOR_WRITE.  This bug is fixed in 5.1.