found via `codespell-q 3`
please review

whose names differ only in case; this causes problems with some platforms
(github issue #172).

IEND chunks, too, but although no application will read them, they give humans
something to look at.

in the contrib/testpngs/crashers directory.

Make pngtest --strict, --relax, --xfail options imply -m (multiple).

Moved testing of bad pngs into a separate tests/pngtest-badpngs script
Added the --xfail (expected FAIL) option to pngtest.c. It writes XFAIL
    in the output but PASS for the libpng test.

Back ported from libpng 1.7
Signed-off-by: NJohn Bowler <jbowler@acm.org>