tests/narrow-library.sh

updatecaches: use the caches argument in `hg debugupdatecaches`

This is the new way.

Differential Revision: https://phab.mercurial-scm.org/D10729

cat >> $HGRCPATH <<EOF
[extensions]
narrow=
[ui]
ssh="$PYTHON" "$RUNTESTDIR/dummyssh"
[experimental]
changegroup3 = True
EOF