pgsql: Re-enable pg_terminate_backend() using SIGTERM.

Log Message:
-----------
Re-enable pg_terminate_backend() using SIGTERM.  SIGTERM testing still
needed.

Modified Files:
--------------
    pgsql/doc/src/sgml:
        func.sgml (r1.432 -> r1.433)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/func.sgml?r1=1.432&r2=1.433)
        runtime.sgml (r1.413 -> r1.414)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/runtime.sgml?r1=1.413&r2=1.414)
    pgsql/src/backend/utils/adt:
        misc.c (r1.61 -> r1.62)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/misc.c?r1=1.61&r2=1.62)
    pgsql/src/include/catalog:
        pg_proc.h (r1.491 -> r1.492)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/pg_proc.h?r1=1.491&r2=1.492)
    pgsql/src/include/utils:
        builtins.h (r1.314 -> r1.315)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/builtins.h?r1=1.314&r2=1.315)