Update CREATE FUNCTION documentation about argument names.
Update CREATE FUNCTION documentation about argument names.

The 9.2 patch that added argument name support in SQL-language functions
missed updating a parenthetical comment about that in the CREATE FUNCTION
reference page.  Noted by Erwin Brandstetter.

yazun/postgres-xl,yazun/postgres-xl,adam8157/gpdb,techdragon/Postgres-XL,oberstet/postgres-xl,jmcatamney/gpdb,50wu/gpdb,xinzweb/gpdb,jmcatamney/gpdb,ashwinstar/gpdb,oberstet/postgres-xl,lisakowen/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,50wu/gpdb,jmcatamney/gpdb,adam8157/gpdb,jmcatamney/gpdb,ovr/postgres-xl,zeroae/postgres-xl,adam8157/gpdb,Postgres-XL/Postgres-XL,lisakowen/gpdb,50wu/gpdb,ashwinstar/gpdb,lisakowen/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,yazun/postgres-xl,pavanvd/postgres-xl,lisakowen/gpdb,greenplum-db/gpdb,ovr/postgres-xl,greenplum-db/gpdb,techdragon/Postgres-XL,jmcatamney/gpdb,oberstet/postgres-xl,adam8157/gpdb,Postgres-XL/Postgres-XL,xinzweb/gpdb,adam8157/gpdb,ovr/postgres-xl,xinzweb/gpdb,Postgres-XL/Postgres-XL,adam8157/gpdb,ashwinstar/gpdb,pavanvd/postgres-xl,techdragon/Postgres-XL,yazun/postgres-xl,lisakowen/gpdb,oberstet/postgres-xl,50wu/gpdb,lisakowen/gpdb,adam8157/gpdb,techdragon/Postgres-XL,adam8157/gpdb,jmcatamney/gpdb,xinzweb/gpdb,50wu/gpdb,zeroae/postgres-xl,50wu/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,techdragon/Postgres-XL,xinzweb/gpdb,oberstet/postgres-xl,greenplum-db/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,pavanvd/postgres-xl,lisakowen/gpdb,yazun/postgres-xl,xinzweb/gpdb,pavanvd/postgres-xl,zeroae/postgres-xl,pavanvd/postgres-xl,xinzweb/gpdb,zeroae/postgres-xl,xinzweb/gpdb,ovr/postgres-xl,greenplum-db/gpdb,zeroae/postgres-xl,50wu/gpdb,ashwinstar/gpdb,ovr/postgres-xl,jmcatamney/gpdb,jmcatamney/gpdb,lisakowen/gpdb,Postgres-XL/Postgres-XL,Postgres-XL/Postgres-XL,50wu/gpdb