A few new Pigeonhole features

[Stephan Bosch]

Hi,

A few new Pigeonhole features that enthusiasts can experiment with:

- Recently, I implemented support for the "imapsieve" extension in Sieve 
and its IMAP counterpart (https://tools.ietf.org/html/rfc6785). This is 
now in the Pigeonhole master branch. This allows running Sieve scripts 
at IMAP activity, rather than at delivery. There are also facilities for 
the familiar sieve_before/sieve_after administrator scripts. The 
documentation is currently only in the sources and not on the wiki:

https://raw.githubusercontent.com/dovecot/pigeonhole/master/doc/plugins/imapsieve.txt

- Yesterday, I implemented online trace debugging for Sieve scripts: 
i.e., directly during delivery rather than only using the sieve-test 
tool. This is also supported for the IMAPSIEVE feature discussed above. 
This is documented in the INSTALL file:

https://github.com/dovecot/pigeonhole/blob/master/INSTALL#L522



In other news, I started a specification for a new Sieve feature that 
allows using the IMAP SPECIAL-USE attributes from Sieve scripts:

https://tools.ietf.org/html/draft-bosch-sieve-special-use-00

There is no implementation yet.


Any comments, suggestions or bug reports are welcome.

Regards,

Stephan.