to stop some Coverity issues (162705, 162706, and 162707).

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

in the contrib/testpngs/crashers directory.

with "II" or "MM".

to account for the minimum 'deflate' stream.

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

num_exif argument to png_get_eXIf_1() (Github Issue 171).

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.

function (Suggested by Max Stepin).

bytes too small (neglected to account for a partial DEFLATE buffer)

no longer using deprecated cmake LOCATION feature (Clifford Yapp).

a limit for some files.