The previous coding tried to handle possible failures when fsyncing a
tty or pipe fd by accepting EINVAL - but apparently some
platforms (windows, OSX) don't reliably return that. So instead check
whether the output fd refers to a pipe or a tty when opening it.

Reported-By: Olivier Gosseaume, Marko Tiikkaja
Discussion: 559AF98B.3050901@joh.to

Backpatch to 9.4, where pg_recvlogical was added.