Adding a CouchDB backend

[Théodore Biadala]

(looks like my previous mail didn't go through)

Sorry for the line length.

> I ask contributors to send patches as plain emails to make the review
> as easy as possible.

It's pretty long and it's new files, so I thought this would be 
"cleaner". I'll know it for next time.


> I'm not sure: do you know we are slowly moving to the (currently
> supported) sqlite backend? Of course, it doesn't mean we couldn't
> support other backends.

I saw that on the ml but as Daniel said, couchdb is for mail storage 
not for sync status.


> So, I have to ask you what is your first intent in adding support for
> CouchDB?

With couchdb you can replicate very easily. Makes backup really simple. 
And I want to use couchdb as a mail reader later. Putting everything in 
couch mean It's easier to use than maildir or IMAP for me.


--
Théodore Biadala