tests/narrow-library.sh

diffhelpers: be more tolerant for stripped empty lines of CRLF ending

Exchange. It appears to trim lines containing only whitespace as well as
converting LF to CRLF.

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