Small bugfix : elimination of spurious linefeeds.

The foo-concordance.tex file resulting from compilation of a
not-so-small foo.tex file may contain spurious " \%\n" groups (in
regexp parlance) which are equivalent to " " fot TeX and friends.

These are a pain to parse with regexps, so the best thong is to purge
them from the buffer before parsing with a swift gsub...

Emmanuel Charpentier, 26-XII-2014