Changes in v2.12

Adjusted the build/test environment for .NET 4.5.2 to use the 4.5.1 task runner instead of the 4.5.3 
task runner.  This is because .NET 4.5.3 is not yet installed on all systems.

Adjusted the XUnit V2 framework utilisation type so that it now defaults to DynamicAnalysis.  This has 
been done to provide more reliable compatibility when working with this framework, as not all features 
can be made to work correctly under StaticAnalysis.

Fixed an issue that was preventing NCrunch from correctly identifying the entry points of tests in MSpec 
under VS2015.