tests/narrow-library.sh

scmutil: extract function that builds revset expr to select bookmark branch

This is needed to process "log -B" option properly. "log" options have to
be translated to a revset expression, not to an evaluated set.

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