[fetch] RequestCache "no-cache" type must also set the right headers (#232)

Again, similar to #201.

When always validating the contents of the cache, Gecko sends `Cache-Control: max-age=0` to signal to the HTTP proxies along the way to revalidate their cached entries.  This is the behavior for HTTP/1.1.  For HTTP/1.0, Gecko only sends `Pragma: no-cache` since there is no better header to send.

I think we should spec the HTTP/1.1 behavior.

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Reply to this email directly or view it on GitHub:
https://github.com/whatwg/fetch/issues/232