[exim] CHUNKING support

Hi,

Dedicated followers of the Exim codebase will have noted the appearance
of support for CHUNKING (RFC3030).

If there are any bleeding-edge sites out there set up to take
performance measurements, I'd love to hear your comments.
Google and Hotmail are the two majors I see talking CHUNKING,
and at least one Apple MUA.


I have one other possible mod in mind - storing the spoolfile
in (CRLF) wire-format - but that demands more thought. It would
help most on store-and-forward nodes, and only when the inbound
transfer used CHUNKING.
- --
Cheers,
Jeremy