RCR 130: Provide a common ancestor for GetoptLong error classes

Witha little tweaking, the exception mechanism of GetoptLong could be made a lot more convenient,

As I understand it the parsing stage of GetoptLong can throw one of four errors:

• GetoptLong::AmbigousOption
• GetoptLong::NeedlessArgument
• GetoptLong::MissingArgument
• GetoptLong::InvalidOption

The annoyance? They don't have a common yet unique parent. They all inherit from StandardError instead of, ideally, inheriting from something along the lines of a GetoptLong::Error. So, instead of being able to do:

begin
  GetoptLong.new().set_options(
                               [ ... ]
                               ).each ...
rescue GetoptLong::Error
  printHelp()
  exit 1
end

I seem to have to do something like:

begin
  GetoptLong.new().set_options(
                               [ ... ]
                               ).each ...
rescue GetoptLong::AmbigousOption, GetoptLong::NeedlessArgument,
       GetoptLong::MissingArgument, GetoptLong::InvalidOption
  printHelp()
  exit 1
end

That feels a little clumsy. I wonder if there is some reasoning behind this or would it make sense to change GetoptLong so that there is a catch-all parent class for the errors that it can throw?