The Windows coding of ShutdownWorkersHard() thought that setting termEvent
was sufficient to make workers exit after an error.  But that only helps
if a worker is busy and passes through checkAborting().  An idle worker
will just sit, resulting in pg_dump failing to exit until the user gives up
and hits control-C.  We should close the write end of the command pipe
so that idle workers will see socket EOF and exit, as the Unix coding was
already doing.

Back-patch to 9.3 where parallel pg_dump was introduced.

Kyotaro Horiguchi