Relax pngtest-all message testing

Previously the 'make check' test pngtest-all looked for given messages
at EOL.  The match failed with Windows/MSYS2 because of the Windows
<cr><lf> line endings output by pngtest.  This changes the test to look
for the message anywhere in a line; this might give false matches but
the specific messages being searched for are not likely to cause this
problem.

Signed-off-by: John Bowler <jbowler@acm.org>
1 file changed