tests/narrow-library.sh

dirstate-v2: shrink on-disk path lengths to 16-bits

Differential Revision: https://phab.mercurial-scm.org/D11091

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