Enable native IDN support in Ruby 1.9.

I ported the old [idn](http://rubygems.org/gems/idn) gem to Ruby 1.9 in the [idn_one_nine](https://github.com/bradcater/idn_one_nine) gem. I haven't pushed it to RubyGems as a "proper" gem yet, as it's still lacking documentation. Since it's purely a port to be compatible with the 1.9 API versus the old 1.8 API (and porting the tests from Test::Unit to RSpec), the interfaces should "just work."

Would you be interested in incorporating the [idn_one_nine](https://github.com/bradcater/idn_one_nine) gem in addressable if I get it packaged up and on the usual gem hosts? If so, I'll get that done.