In the case of empty Etags, I think that sending an empty header has been shown to be the wrong choice. I suggest it should be removed from the head and the 2_7 branch.
For future reference to any committers: if you modify any HTTP headers sent by Zope, you very likely ought to discuss it before checking it in.
Along with that the "MS Author Via" header garbage should at least be governed by some configuration flag.
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