pgsql: Clarify documentation that initdb -A or editing pg_hba.conf is

Log Message:
-----------
Clarify documentation that initdb -A or editing pg_hba.conf is required
if you do not trust local users.

Modified Files:
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pgsql/doc/src/sgml:
installation.sgml (r1.283 -> r1.284)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/installation.sgml.diff?r1=1.283&r2=1.284)