Fix the .net40 tests:
Wow. Razor2 has an SecurityTransparent assembly attribute, which later versions do not have. This is/was the root for a lot of confusion. This also means that now our .net40 lib is not binary compatible anymore with Razor3 (and the other way around).

See http://msdn.microsoft.com/en-us/library/dd233102.aspx for details. We now need to ensure that RazorEngine and (especially) Razor are loaded with full trust.