[Dovecot] compact folders, expunge, etc

[Gregory Bond]

Mail Admin wrote:

>Thunderbird continues to behave erratically with dovecot test builds.  I
>haven't been able to test the imap_client_workarounds=tb-negative-fetch
>option yet as I'm still running test52.  Thunderbird displays blank
>messages when they are opened, but "Edit as new" shows the message
>contents. 
>
I'm also seeing this very occasionally.

I'm pretty sure its a TB bug as looking at the same maildir via 
Mutt/dovecot shows the proper contents.   My guess is it's the same 
underlying bug that the tb-negative-fetch workaround helps, and that for 
some reason TB is caching bogus information about that UIDL.  I haven't 
yet worked out how to flush TB's header cache and re-fetch all the 
headers (short of removing dovecot's index files....)

Refiling the busted message to a new folder then back again fixes it.