- Use IDNA properties from Unicode 6.3.0. Internet Architecture Board (IAB)
  issued statement recommending against the use of Unicode 7.0.0 until
  issues relating to U+08A1 codepoint are resolved. See http://goo.gl/Ed1n0K
- Identify some cases when label would be too longer to be a legal DNS name
  and raise an exception. (Thanks, Ed Lewis)