[imp] purging messages in IMP/DIMP

[Liam Hoekenga]

This is with IMP / DIMP on HEAD.

We've had some users complain that the "purge deleted" action in DIMP 
isn't actually purging email. (I've seen it in IMP too.)  It notifies the 
user that messages were purged, but they sometimes aren't.  If I check 
with another client, I'll find the messages may not have even been marked 
deleted.

I'm turning of $conf['mboxcache']['use_mboxcache'] and 
$conf['mlistcache']['use_mlistcache']  for the time being to see if it 
helps.

Anyone else notice wonky messages deletion / purging?

Liam