tests/narrow-library.sh

tests: don't hard-code /bin/bash

From Thomas Klausner in pkgsrc.

Differential Revision: https://phab.mercurial-scm.org/D10507

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