Added conditionals to the mock C++ projects to build with whatever version of the C++ tools chain that it finds
Removed unneeded build platforms from the solution.
Simplified the toolset conditional code since we cannot build on 2010 because of async.
The C++ projects are now building using msbuild from a Visual Studio command line
Merge pull request #268 from nunit/issue-246

Issue 246 - C++ Tests do not compile in VS2013