_values' options

[Oliver Kiddle <opk@xxxxxxxxxxxxx>]

_values, currently doesn't handle any of the standard compadd style
arguments. This means that it can't be used from _arguments. Try this
to see why:
  _arguments '-a:val:_values -s , value one two three'

I do actually have a case where _values would be useful from
_arguments. I'm guessing that all it would need is a zparseopts to
throw the options away?

The other related issue is that _values' -S option is possibly not the
best choice of letter. Ideally, it would be possible to pass _values a
suffix and it would work out when the value being completed is the last
possible value (from the exclusion lists) and then use that suffix.

Oliver