pgsql-server: Code review for recently-added network functions.

Log Message:
-----------
Code review for recently-added network functions.  Get it to work when
log_hostname is enabled, clean up documentation.

Modified Files:
--------------
    pgsql-server/doc/src/sgml:
        func.sgml (r1.206 -> r1.207)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/doc/src/sgml/func.sgml.diff?r1=1.206&r2=1.207)
    pgsql-server/src/backend/utils/adt:
        network.c (r1.50 -> r1.51)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/utils/adt/network.c.diff?r1=1.50&r2=1.51)
    pgsql-server/src/include/catalog:
        pg_proc.h (r1.335 -> r1.336)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/include/catalog/pg_proc.h.diff?r1=1.335&r2=1.336)
    pgsql-server/src/include/utils:
        builtins.h (r1.241 -> r1.242)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/include/utils/builtins.h.diff?r1=1.241&r2=1.242)