windows: handle file-like objects without isatty() method
Copying the function is not nice, but moving around stuff to avoid the
circular import didn’t seem to be worth the effort.
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"phabricator.uri": "https://phab.mercurial-scm.org/",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}