vfs: suppress some pytype errors around us using a private attribute
Looking at threading._MainThread seems like we're probably a little
unsupported, but since this code appears to work on both Python 2 and
3 I'm not going to sweat this for now.
Differential Revision: https://phab.mercurial-scm.org/D7282
#require serve
$ hg clone http://localhost:$HGPORT/ copy
abort: * (glob)
[255]
$ test -d copy
[1]
$ "$PYTHON" "$TESTDIR/dumbhttp.py" -p $HGPORT --pid dumb.pid
$ cat dumb.pid >> $DAEMON_PIDS
$ hg clone http://localhost:$HGPORT/foo copy2
abort: HTTP Error 404: * (glob)
[255]
$ killdaemons.py