Issue 215 - Running 32-bit tests on a 64-bit OS

This works with some caveats.

1. You cannot use `--process=Single`, you must run Separate or Multiple.
2. If you are passing in multiple test assemblies and they are not all the same architecture, you must use `--process=Multiple`

I think this is reasonable and we can add it to the FAQ.

I added two C++ mock test assemblies to the solution for testing architecture. C++/CLI has a different header format than C#. I have set them to not build under mono and the tests check if the assemblies exist. The projects don't load under Xamarin, but that is no different than the SilverLight projects.
Stashing this flag in the RuntimeFramework seems a bit opportunistic. The bitness of the process is orthogonal to the framework involved. Of course, these are our own logical constructs, but if we elect to have a construct that includes the bitness, then all of RuntimeFramework's operations should probably take it into account.

Isn't this really an attribute of the ProcessRunner rather than the framework?