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).