pgsql: Mention actual function names in documentation of how to pass

Log Message:
-----------
Mention actual function names in documentation of how to pass binary
values to libpq.

Modified Files:
--------------
pgsql/doc/src/sgml:
libpq.sgml (r1.259 -> r1.260)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/libpq.sgml?r1=1.259&r2=1.260)