Fixed Swift compatibility to Xcode 6 Beta 3:

- Fixed array types
- Dropped support for explicit NilType (which no longer exists).
- Currently expect(nil) is NOT supported.
Updated test script to kill iOS sim before running.

xcodebuild test will fail if the iOS simulator is in a non-responsive
state to the remote client (aka, xcodebuild). Explicitly closing
the simulator before running tests will prevent this issue from
surfacing in command line test runs.