Please fill in this template when reporting a bug, unless you know what you
are doing.
Description of Problem:

When viewing mails in Threaded mode sorted by date, Evolution sorts the
threads by date of the first mail in the thread.  That means that
long-running threads or threads that are resurrected after a long time are
hard to find -- I often find myself scrolling through my entire mailbox to
find that one unread mail that just came in.  If they were sorted by
'thread with newest mail in it first' order, you'd be able to see all
activity up in the top.

In particular this is a problem because there's no way to sort by
read/unread, AFAICS.

Steps to reproduce the problem:
1. Get a lot of mail in long-time threads.
2. Click on 'Date' to get the list sorted by date.
3. 

Actual Results:
Threads are sorted by first date, leaving new messages arbitrarily far down
the mailbox.

Expected Results:
The threads with new messages should be at the top, easy to find.

How often does this happen? 
Always.

Additional Information:
Gnus does its threading this way, and I really, really prefer that.