Comment 2 for bug 747159

Your original method for getting thread-folding information was by
analyzing the Summary buffer. I have now added a folded-flag in the
message attributes and changed it to get the information from there.
The new method should be more reliable in the long run. But we need
to get the bugs out first.

In the example I ran into, there was a thread that looked like:

  + 21+1 ...
      22 ...

I deleted and expunged 22, then tried to save 21. It turns out that
the folded-flag of 21 is still true. So, VM thinks that it is still
the root of a thread. I have vm-enable-thread-operations set to 'ask.
So, VM asks whether it should save all the messages in the thread
(even though there is only one message in the thread now).

I did a quick fix to `vm-thread-root-p' by saying that a message
should be regarded as a root only if it has more than one message in
the thread.

But perhaps the folded-flag should be set to nil when the rest of its
thread gets expunged. I haven't come to a resolution on that issue
yet.

This bug report merely says that we should test out all the
implications of moving to the folded-flag so that the we can get the
bugs out.

Cheers,
Uday