buffer: make byteLength work with ArrayBuffer & DataView

Convert anything to string, but Buffer, TypedArray and ArrayBuffer

```
var uint8 = new Uint8Array([0xf0, 0x9f, 0x90]);
Buffer.byteLength(uint8); // should be 3, but returns 11
Buffer.byteLength(uint8.buffer); // should be 3, but return 20
```

PR-URL: https://github.com/nodejs/node/pull/5255


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>