crecord: null out the curses attribute with `None` on failure to import
Pytype got really confused that this could be `Union[module, bool]`, and spewed
about tons of attributes that are not available on `bool`.
Differential Revision: https://phab.mercurial-scm.org/D10210
cat >> $HGRCPATH <<EOF
[extensions]
narrow=
[ui]
ssh=$PYTHON "$RUNTESTDIR/dummyssh"
[experimental]
changegroup3 = True
EOF