pgsql: Return proper exit code (3) from psql when ON_ERROR_STOP=on and

Log Message:
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Return proper exit code (3) from psql when ON_ERROR_STOP=on and
--single-transaction are both used and the failure happens in commit,
e.g. failed deferred trigger.  Also properly free BEGIN/COMMIT result
structures from --single-transaction.

Per report from Dominic Bevacqua

Tags:
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REL8_2_STABLE

Modified Files:
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    pgsql/src/bin/psql:
        command.c (r1.174 -> r1.174.2.1)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/bin/psql/command.c?r1=1.174&r2=1.174.2.1)