Add pg_audit, an auditing extension

This extension provides detailed logging classes, ability to control
logging at a per-object level, and includes fully-qualified object
names for logged statements (DML and DDL) in independent fields of the
log output.

Authors: Ian Barwick, Abhijit Menon-Sen, David Steele
Reviews by: Robert Haas, Tatsuo Ishii, Sawada Masahiko, Fujii Masao,
Simon Riggs

Discussion with: Josh Berkus, Jaime Casanova, Peter Eisentraut,
David Fetter, Yeb Havinga, Alvaro Herrera, Petr Jelinek, Tom Lane,
MauMau, Bruce Momjian, Jim Nasby, Michael Paquier,
Fabrízio de Royes Mello, Neil Tiffin

doc/src/sgml/contrib.sgml

@@ -124,6 +124,7 @@ CREATE EXTENSION <replaceable>module_name</> FROM unpackaged;
  &ltree;
  &pageinspect;
  &passwordcheck;
+ &pgaudit;
  &pgbuffercache;
  &pgcrypto;
  &pgfreespacemap;