
Calling this function will poison the current transaction.  This means that
it is forced to roll back at when committed.  The code can be
in integer that selects the error message generated when trying to commit.
This is useful before signalling application errors from SQL code that runs
in manual commit mode.  This can ensure that even if the client attempts
a commit after getting the error signalled by the application the transaction
will not commit.

The code should be the constant 6, resulting the in the @transaction
rolled back due to previous SQL Error@.
