Switch tests from using reflection to get values to using internal access.

[karljj1]

Hey.
I'm currently going through the 3.0 features and merging what I can into our version(we use an older version of .net), so I'm reading through all the code at the moment, kind of a mini code review ;)
I noticed that in some tests(ReflectionFormatterTests) you are using reflection to get at internal values to test them. I have found it simpler and safer to use internal access for this use case. E.G Remove GetInstanceField and make the type cache property internal. Then use assembly: InternalsVisibleTo to give your tests internal access.

[axunonb]

Gosh, I remember, This has not found its way from the brain to the to-do list 😉
There should also be a test case for SmartSettings.IsThreadSafeMode enabled / disabled.
Gonna fix that.

[axunonb]

Closed with PR #291