multipart range requests

Ok,
    I don't think that we need full multipart/byteranges support for 3.0
- it's not present on 2.5.

In 2.5, if we do the range ourself, it will also work in the fix-ranges
branch.

However, if we don't do the ranges ourself, then we simply pass through
the object, as a rangeless reply.

So, for 3.0 I plan to do the following:

If we decide not to do ranges on a multipart range request:
* Mark the object as uncachable.
* Delete the range request metadata.

Thoughts?

Rob

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