CLP fix: Use proper return value convention from Clp_OptionError.

Also add %V support. From Click.
Apparently some perls now don't allow \376 as a regex delimiter.
Tumblr found a good GIF with 1 superfluous image pixel.

So handle that case; ignore the superfluous pixel, store the
real pixels, don't warn if only 1 pixel is superfluous, and
the superfluous pixel warning is a warning, not an error.