tests/narrow-library.sh

persistent-nodemap: add test case reproducing a Rust panic

Thanks to Mitchell Plamann for reporting this bug.
The next commit fixes it.

Differential Revision: https://phab.mercurial-scm.org/D9900

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