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.
$ echo "[extensions]" >> $HGRCPATH
$ echo "mq=" >> $HGRCPATH
$ hg init
$ echo 'base' > base
$ hg ci -Ambase
adding base
$ hg qnew -mmqbase mqbase
$ hg qsave
$ hg qrestore 2
restoring status: hg patches saved state