Tidy check on Ubuntu Xenial

[Han-Wen Nienhuys]

In my docker install of Ubuntu Xenial, I see the following failure,
apparently coming from tidy.

creating 
/lilypond/out/test-results/input/regression/out-test-baseline/test-output-distance.png
creating 
/lilypond/out/test-results/input/regression/out-test/test-output-distance.png
Validating 
/lilypond/out/test-results/input/regression/out-test/test-output-distance.details.html
line 6 column 1 - Warning: <meta> proprietary attribute "charset"
line 6 column 1 - Warning: <meta> lacks "content" attribute
line 9 column 1 - Warning: <table> lacks "summary" attribute
make: *** [local-check] Error 1

$ docker run --rm -it lilypond-base-ubuntu dpkg -l tidy
..
ii  tidy                        20091223cvs-1.5    amd64
HTML syntax checker and reformatter


For now, I can work around this by removing tidy, but do we really
need this dependency? It also looks like it introduces some extra
makefile complexity.

-- 
Han-Wen Nienhuys - address@hidden - http://www.xs4all.nl/~hanwen