The use of `let` is unnecessary here, particularly in a
file that is needed to run any of the tests, even the ES5 tests.
Removing it allows older engines to run older tests.

After conversations in #1215, we need to catch up with the code that was previously
produced before we set the features flags requirements.

```
$ python tools/lint/lint.py --whitelist lint.whitelist harness/*.js
Linting 25 files.
Linting complete. 0 errors found.
```

- Renames detachArrayBuffer-$262.detachArrayBuffer.js -> detachArrayBuffer-host-detachArrayBuffer.js (previous naming prevents command-click from terminal)

Signed-off-by: Rick Waldron <waldron.rick@gmail.com>

Expected/actual values should be delimited in a way that
isn't confusable with actual string quotes " '

When invoked without a custom assertion message, `assert.sameValue` and
`assert.notSameValue` automatically create a message that describes the
actual and expected values.

Extend both assertion methods to also include this information in cases
where a custom message has been specified.

Closes #57.

Closes #110