Update GRANT USAGE on schema permission description.

doc/src/sgml/ref/grant.sgml

 <!--
-$PostgreSQL: pgsql/doc/src/sgml/ref/grant.sgml,v 1.57 2006/07/12 15:37:10 momjian Exp $
+$PostgreSQL: pgsql/doc/src/sgml/ref/grant.sgml,v 1.58 2006/07/19 18:42:31 momjian Exp $
 PostgreSQL documentation
 -->
 
@@ -276,8 +276,8 @@ GRANT <replaceable class="PARAMETER">role</replaceable> [, ...]
        schema (assuming that the objects' own privilege requirements are
        also met).  Essentially this allows the grantee to <quote>look up</>
        objects within the schema.  Without this permission, it is still
-       possible to see the object names by querying the system tables, but
-       they cannot be accessed via SQL.
+       possible to see the object names, e.g. by querying the system tables,
+       so this is not a completely secure way to prevent object access.
       </para>
       <para>
        For sequences, this privilege allows the use of the