[fetch] response.bodyUsed is an ambiguous name (#57)

After trying to stub `fetch()` in some unit tests [in this project](https://github.com/gaia-components/serviceworkerware), I came across that `bodyUsed` wasn't what I expected. I thought it was a boolean showing that the response contained a body, instead of a value telling that the body has already been used somewhere in your own code.

[As the specs](https://fetch.spec.whatwg.org/#concept-response) are currently not very explanatory on that particular subject:
> The bodyUsed attribute's getter must return true if the used flag is set, and false otherwise.

I'd suggest to rename `bodyUsed` to `bodyAlreadyUsed`, to make the intent clearer.

What do you all think?

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Reply to this email directly or view it on GitHub:
https://github.com/whatwg/fetch/issues/57