pgsql: Add note cautioning that you can't use an encrypting IDENT server

Log Message:
-----------
Add note cautioning that you can't use an encrypting IDENT server
with Postgres.

Tags:
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REL8_0_STABLE

Modified Files:
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pgsql/doc/src/sgml:
client-auth.sgml (r1.70.4.1 -> r1.70.4.2)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/client-auth.sgml.diff?r1=1.70.4.1&r2=1.70.4.2)