Merge branch 'rs/opt-parse-long-fixups'

Merge branch 'rs/opt-parse-long-fixups'

The parse-options code that deals with abbreviated long option
names have been cleaned up.

Reviewed-by: Josh Steadmon <steadmon@google.com>
cf. <ZfDM5Or3EKw7Q9SA@google.com>

* rs/opt-parse-long-fixups:
  parse-options: rearrange long_name matching code
  parse-options: normalize arg and long_name before comparison
  parse-options: detect ambiguous self-negation
  parse-options: factor out register_abbrev() and struct parsed_option
  parse-options: set arg of abbreviated option lazily
  parse-options: recognize abbreviated negated option with arg