[libpng16] Detect wrong libpng versions linked to pngdeflate, which currently

only works with libpng versions that can be made to reliably fail when
    the deflate data contains an out-of-window reference.  This means only
    1.6 and later.
  Fixed gnu issues: g++ needs a static_cast, gcc 4.4.7 has a broken warning
    message which it is easier to work round than ignore.

contrib/libtests/timepng.c

@@ -252,7 +252,7 @@ int main(int argc, char **argv)
 
          while (fgets(filename, FILENAME_MAX+1, stdin))
          {
-            int len = strlen(filename);
+            size_t len = strlen(filename);
 
             if (filename[len-1] == '\n')
             {