hghave: make error output easier to diagnose
I had a typo that meant the new bash check was throwing an exception
(due to a missing argument), but it was very hard to diagnose without
this change.
Differential Revision: https://phab.mercurial-scm.org/D10733
cat >> $HGRCPATH <<EOF
[extensions]
narrow=
[ui]
ssh="$PYTHON" "$RUNTESTDIR/dummyssh"
[experimental]
changegroup3 = True
EOF