[pysieved] New experimental version

[Neale Pickett <neale at woozle dot org>]

After a long break I've finally implemented changes that should make the 
dovecot auth and dovecot userdb modules play together nicely.  The version 
I've checked in passes most of the unit tests but that of course doesn't mean 
it's going to work, as I haven't given it a real-life test yet.  

Don't install it to your production systems, but any testing I could get on it 
would be great.

If you're interested in writing plugins, they've all been into a "plugins" 
directory, and the three different APIs (auth, userdb, storage) have been 
merged into a single object.  The "auth", "lookup", and "create_storage" 
methods take one argument: a modifiable dictionary.  This will allow plugins 
with an "auth" that sets the home directory in the dictionary, and with a 
simple "lookup" method that returns that directory.

I'm embarrassed to say I'm still not clear on Dovecot authentication.  Could 
somebody maybe write up a README.Dovecot about how to configure Dovecot to do 
what's needed?

Thanks,

Neale