Initial work on NUnit2 XML output listener.

* Add basic --nunit2 filename configuration parameter.
* New NUnit2XmlOutputListener class.
* Unit test that validates against xsd, and verifies quite a bit of
  content.
Switch to using Case.Name in NUnit2 XML.
Merge remote-tracking branch 'origin/master' into nunit2_output_listener

Conflicts:
	src/Fixie/ConsoleRunner.cs
Add parameterless ctor to NUnit2XmlOutputListener.

* New ctor allows NUnit2 output to be added via new --fixie:listener
  parameter, e.g. --fixie:listener Fixie.Listeners.NUnit2XmlOutputListener
Merge pull request #33 from petejohanson/nunit2_output_listener

Initial work on NUnit2 XML output listener.