message: turn off png_test
diff: @@ -58,6 +58,7 @@ ExternalProject_Add(png
  -DCMAKE_VERBOSE_MAKEFILE:BOOL=OFF
  -DCMAKE_INSTALL_PREFIX:STRING=${png_INSTALL}
  -DZLIB_ROOT:STRING=${ZLIB_INSTALL}
  + -DPNG_TESTS:BOOL=OFF
  )
  ## put png includes in the directory where they are expected
  