pngimage: add --list-combos
pngunknown: add --strict to catch warnings
pngvalid-standard: remove the spurious --progressive read (compare with
pngvalid-progressive-standard!)
This patch probably applies to 1.5 and 1.6 (where the tests exist) too.
Signed-off-by: John Bowler <jbowler@acm.org>
scripts. Fixed combination of ~alpha with shift. On read invert alpha,
processing occurred after shift processing, which causes the final values to be
outside the range that should be produced by the shift. Reversing the
order on read makes the two transforms work together correctly and mirrors
the order used on write.
