py3: keep stdout as defined by pycompat in procutil
According to https://docs.python.org/3/library/functions.html#open, it's
not possible to use 1 as buffering argument value in binary mode. This
is probably why line buffering does not work well in python3.
On the other hand, sys.stdout.buffer appears to be line-buffered already
on python3. So by not replacing it, there should be no behavior change.
This fixes buffering issue in "hg email" (confirmation prompt shown
before information to be confirmed).
(binary:application/octet-stream)