Expunge labels and dealing with expunges at the beginning of the folder

[Philip Van Hoof <spam pvanhoof be>]

This commit is highly experimental and will need testing.

For testing I recommend doing the following with and without these
changes:

o. Append a bunch of items in an empty folder
o. Open it in tny (the folder)
o. Click outside of the folder in tny (select another folder)
o. Delete a few messages with the lowest UID using another E-mail client
   from the folder
o. Click the folder in tny

Tinymail used to simply re-fetch all, marking all as expunged in the
process, re-retrieving all.

With this patch will Tinymail try harder to keep the not-really expunged
summary info by counting how many removals we had, and shifting the
lists in such a way that we'll just compare assuming that the removal
will soon happen locally too.

http://tinymail.org/trac/tinymail/changeset/3299

Therefore reducing local expunges and .. bandwidth. Although bandwidth
ain't the reason for this one. Rather, getting rid of those "Expunged"
labels.

It's tricky, so everybody who's into this can of course review the
commit. It'll need testing obviously.


-- 
Philip Van Hoof, freelance software developer
home: me at pvanhoof dot be 
gnome: pvanhoof at gnome dot org 
http://pvanhoof.be/blog
http://codeminded.be