aupg - aupg_src: Changed write table to be primary key'ed on transaction

Log Message:
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Changed write table to be primary key'ed on transaction id and timestamp.
Fixed a bug where multiple writes could possibly have been logged for a single
transaction id / timestamp combo.

Modified Files:
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aupg_src/sql:
audit_infrastructure.sql (r1.8 -> r1.9)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/aupg/aupg_src/sql/audit_infrastructure.sql.diff?r1=1.8&r2=1.9)