pgsql: Document that SSL is only possible on tcp/ip connections in the

Log Message:
-----------
Document that SSL is only possible on tcp/ip connections in the
postgresql.conf 'ssl' section.

Modified Files:
--------------
pgsql/doc/src/sgml:
config.sgml (r1.192 -> r1.193)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/config.sgml?r1=1.192&r2=1.193)