Transport.*_multi functions should be removed

[John A Meinel]

A long long time ago, I had an idea about how to improve streaming performance without a smart server. We would allow the Transport.*_multi, etc functions take a generator, and yield a generator. Which would allow us to prefetch many files in one request. Thus things like "stat_multi" and "get_multi" were born.

However, we've decided that the only smart way forward is a real custom server protcol. And, in fact, only "Store.copy_multi" is used in real code, and IIRC Store is only used for the really-really-really old formats (pre weave).

They should be shot and buried, so that our test suite doesn't suffer for them.