304 response should contain etag

[vicky1999]

Solves #3286

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[Conduitry]

I don't think we need to include content-type or any of the other headers in response.headers. We can probably move response.headers['etag'] = etag; back where it was, and do headers: { etag } here instead.

[vicky1999]

okay

[vicky1999]

only etag is added to the response if it is a 304 response

[Rich-Harris]

On a closer reading of the original thread, we do need to preserve headers, but only certain ones. I've updated this branch. Thanks!

[Maggi64]

Yes that looks like it would fit the spec, thanks!