Squashed 'External/BuildScripts/' content from commit a0b0763

git-subtree-dir: External/BuildScripts
git-subtree-split: a0b0763d260c98919b44e621c1a4229698391c99
Merge commit '2177e77834fe52e3443bff751e2a03e8a6e4d281' as 'External/BuildScripts'
Switched Swum.NET over to the new build script.
Added a nuspec package for ABB.Swum.dll.
Added NuGet to the externals directory.
Removed old build scripts.
Updated nunit nuget packages to 2.6.3.
Added a RestorePackages target that executes prior to build & test.
Changed relative paths in the performance tests to work relative to the common build directory.
Dummy commit for the release branch.
Force MSBuild to use version 4.0 in the build file.
Merge branch 'master' into srcml40-integration

Conflicts:
	ABB.Swum.Tests/packages.config