Buffer.prototype.toLocaleString needs a Buffer-specific implementation

[jasnell]

The toLocaleString() method is intended to provide a locale-sensitive toString() variant for various types.

> Buffer.prototype.toLocaleString === Uint8Array.prototype.toLocaleString
true
> Buffer.from('test').toString()
'test'
> Buffer.from('test').toLocaleString()
'116,101,115,116'
>

Buffer's toLocaleString() is inherited from Uint8Array which makes it less than useful. For the time being, it should likely simply defer to toString() using the default platform charset.

/cc @trevnorris @srl295 @addaleax

(PR incoming soon)