RFC5703 support (Sieve Email Filtering)

[Robert Mueller]

> I want to check how many people out there would be interested on
> RFC5703 support in Cyrus IMAP, that is, Sieve Email Filtering: MIME
> Part Tests, Iteration, Extraction, Replacement, and Enclosure.
> 
> See: http://tools.ietf.org/html/rfc5703

Any improvements to cyrus sieve support would be highly welcomed!

Apart from some charset improvements that fell out of other work, I
believe there really hasn't been any work on cyrus sieve recently, and
it would be great to kick start that.

Cheers

Rob