pgsql: Restrict pgstattuple functions to superusers.

Log Message:
-----------
Restrict pgstattuple functions to superusers. (This might be too strict,
but no permissions check at all is certainly no good.) Clean up usage
of some deprecated APIs.

Modified Files:
--------------
pgsql/contrib/pgstattuple:
pgstatindex.c (r1.6 -> r1.7)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/pgstattuple/pgstatindex.c?r1=1.6&r2=1.7)
pgstattuple.c (r1.27 -> r1.28)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/pgstattuple/pgstattuple.c?r1=1.27&r2=1.28)
pgstattuple.sql.in (r1.13 -> r1.14)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/pgstattuple/pgstattuple.sql.in?r1=1.13&r2=1.14)
uninstall_pgstattuple.sql (r1.3 -> r1.4)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/pgstattuple/uninstall_pgstattuple.sql?r1=1.3&r2=1.4)