pgsql: Make the new pg_stat_get_activity use OUT parameters, so you

Log Message:
-----------
Make the new pg_stat_get_activity use OUT parameters, so you don't have to
specify the column names and types. Also simplifies the view.

Per comments from Tom.

Modified Files:
--------------
    pgsql/src/backend/catalog:
        system_views.sql (r1.50 -> r1.51)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/catalog/system_views.sql?r1=1.50&r2=1.51)
    pgsql/src/include/catalog:
        catversion.h (r1.456 -> r1.457)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/catversion.h?r1=1.456&r2=1.457)
        pg_proc.h (r1.497 -> r1.498)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/pg_proc.h?r1=1.497&r2=1.498)