Libpng 1.7 supports read without PNG de-interlace, however this means the old
checks on whether contrib/libtests/timepng.c (just checking for sequential read)
are inadequate. 1.7 also provides macros to explicitly turn off png_read_png
and png_read_image, so use these instead.
Signed-off-by: John Bowler <jbowler@acm.org>
handling png_struct members rearranged - partly to reorder to avoid packing,
partly to put frequently accessed members at the start and partly to make
the grouping more clear. png_set_filter code has been rewritten and the
code shared with png_write_start_row moved to a common function. Comments
in png.h have been made more clear. Minor fixes to
contrib/libtests/timepng.c and some of the png_*_tRNS logic, including
more error detection in png_set_tRNS.
