aupg - aupg_src: Added support for multi-column primary keys.

Log Message:
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Added support for multi-column primary keys.
Reoriented the tuple (row value text) storage to store /previous/
values instead of duplicating the current value in the audited table.
Added TG_OP (operation type) tracking.
Added tracking of pg xid (for possible use in conjunction with st timestamp
for future tracking of legitimized transactions).

Need to write more tests, especially for overlapping alterations of
a row by two sessions (make sure no deadlocks). I don't think there will
be locks but I think that you might have confusing entries in the log.

Modified Files:
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aupg_src/sql:
audit_infrastructure.sql (r1.2 -> r1.3)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/aupg/aupg_src/sql/audit_infrastructure.sql.diff?r1=1.2&r2=1.3)