added CodeLocation to native function errors
added ErrorMessageException
refactored FileSystemError into FileSystemException that extends ErrorMessageException and FileSystemError that extends Error
Message no longer extends RuntimeException
renamed classes in .message.message package
added CodeMessage.codeLocation()
added WrappedCodeMessage
extended TestMessageListener.assertOnlyOneProblem() to handle WrappedCodeMessage
refactored SandboxImpl to wrap reported Messages into WrappedCodeMessage
renamed CallLocation -> TaskLocation
renamed InvokeTask -> NativeCallTask