Log Message:
-----------
Add example for pg_config --configure.
Modified Files:
--------------
pgsql/doc/src/sgml/ref:
pg_config-ref.sgml (r1.19 -> r1.20)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/pg_config-ref.sgml.diff?r1=1.19&r2=1.20)