Back xUnit.net Test Support 2.1.7

Notes

Don't crash if we get badly formatted exception data from xunit1 (#50)

From previous builds:
• Support for xunit 2.0
• Rewritten the core runner to be more robust with multi-threading. Should fix issues with aborted or inconclusive tests (#44, #31)
• Updated external annotations for xunit 2.0 (#30)
• Read xunit 2.0 settings from config file (#40)
• Report diagnostic messages when 'xunit.diagnosticMessages' is set in config (#28)
• Report mismatched pre-release versions on failure (#23)
• Fixed crash working with xUnit.net 1.1
• Fixed an issue (#9) to run individual methods, rather than all methods in the class
• Fixed an issue (#21) with Unicode characters in display names and data attributes
• Captures output from ITestOutputHelper
• Shadow copy cache clean up on abort
• Parallelisation re-enabled!

Known issues:
• Live Templates for Theory use xunit1 namespace