[Dovecot] 2.1.x changes and dsync -- Wiki suggestion

[Jeff Kletsky]

There are a couple things that show up on the Upgrading/2.1 wiki page 
that would be useful to have on pages describing dsync (Tools/Dsync, 
Migration/MailFormat, Tools, perhaps others):

* dsync was merged into doveadm
* You can't dsync 2.0.x to/from 2.1.x

That second point is especially "interesting" to me as it seems that 
Apple MacOS X Server is still on 2.0.16, at least from what I see on 
opensource.apple.com. I was planning on migrating mail off the current 
server onto my friend's new MacMini, but I'll have to figure out how to 
"downgrade" the mail jail to a 2.0 version, it seems.

Thanks for all the great work,

Jeff