Rename setup_cancel_handler in pg_dump

Hi,

Attached is a simple patch to rename setup_cancel_handler()
in pg_dump/parallel.c.

I am proposing it because there is a public function with
the same name in fe_utils/cancel.c. I know pg_dump/parallel.c
does not include fe_utils/cancel.h, so there is no conflict,
but I think it is better to use different names to reduce
possible confusion.

I guess there was no concerns when setup_cancel_handler in
pg_dump/parallel.c was introduced because the same name
function was not in fe_utils that could be used in common
between client tools.. The public setup_cancel_handler in
fe_utils was introduced in a4fd3aa719e, where this function
was moved from psql.

Regards,
Yugo Nagata

--
Yugo NAGATA <nagata(at)sraoss(dot)co(dot)jp>