tests/narrow-library.sh

py3: do not pass a memoryview to bdiff.bdiff()

This doesn't look nice, but I don't know how to make a zero-copy slice of
bytes which is compatible with the buffer protocol.

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