[Dovecot] Sieve_extprograms plugin for Pigeonhole v0.3

[Stephan Bosch]

As indicated in the release announcement of Pigeonhole v0.3.0, there is 
also a new experimental plugin available for Pigeonhole v0.3: the 
sieve_extprograms plugin. This can be used to pipe messages to and 
filter messages through external programs (shell scripts). Also, string 
data can be retrieved from such external programs. The plugin can 
currently only be obtained from its Mercurial repository:

http://hg.rename-it.nl/pigeonhole-0.3-sieve-extprograms

Refer to the INSTALL and README files for more information:

http://hg.rename-it.nl/pigeonhole-0.3-sieve-extprograms/raw-file/tip/INSTALL
http://hg.rename-it.nl/pigeonhole-0.3-sieve-extprograms/raw-file/tip/README

The vendor-specific Sieve language extension provided by this plugin are 
documented here:

http://hg.rename-it.nl/pigeonhole-0.3-sieve-extprograms/raw-file/tip/doc/rfc/spec-bosch-sieve-extprograms.txt

Please test this plugin. The plan is to include it into the main 
Pigeonhole release eventually.

Regards,

Stephan.