Issue 54 - Store message and stack trace in `TestContext` (for use in `[TearDown]`)

I added the following read-only properties to `TestContext.CurrentContext.Result` => `Message`, `StackTrace`, `FailCount`, `PassCount`, `SkipCount` and `InconclusiveCount`.

I have unit tests for the passing cases in a `[TearDown]` and in a `[OneTimeTearDown]`.

I have tested `Message`, `StackTrace` and `FailCount` in the debugger, but I can't figure out how to write proper unit tests for them. How do I write fully exercised failing unit tests that pass?

The first half of the TestContext changes are just code style changes. The real changes start at line 341.
Comment is obsolete. We haven't supported CF 1.0 for a while.