[imp] Sort by Thread Patch

[Michael Cochrane]

Quoting Michael Cochrane <mike@graftonhall.co.nz>:

> As I said, it's a quick go at it.. 
> 
> Side Effect / Bug:
> The hide deleted preference is ignored as there's no way to tell imap_thread
> what flags you want. I guess each message could be checked before being added
> into the $sorted array but this seems like a huge cost.
> 

Okay I have updated the patch so it now does this. There isn't a noticable time 
difference on my server (win2k ,low load, but testing with 1000+ msg folders), 
between hiding deleted messages and showing when check isn't done.

http://www.graftonhall.co.nz/mikes/Horde%20Diffs/Sort%20By%20Thread/Head/

- Mike