NBT_DatagramService.py: Pass doctest under Python 2.6.

  * Changed some string formatting patterns to conform with Python 2.6
    expectations.
  * Cleaned up and commented the doctest lines in the Defrag() class.
  * Small improvements to the module doctext.
  * Several minor code formatting changes.
NBT_NameService.py: Small cleanups.
  AddressRecord.dump():
  * Added a missing newline character to the final line of the string
    output.
  * Slightly modified the indentation of the subfields.
  * Added doctest to the class description to test the dump() output.

  Other cleanups:
  * Fixed some incorrectly escaped characters in some docstrings.
  * Condensed two doctest lines to one.