unwind support for Linux 2.6 vsyscall DSO

[Andrew Cagney]

>> I knew.  Unfortunately, it's often proven inadequate, hence
>> there are separate queries for threads etc.
>> 
>> Maybe if to_query had been designed as an iterator in the first place...
> 
> 
> Its interface is wholly vague, so a given query could encode any kind of
> interface you want.  Iteration is easily expressed in such an interface
> either just by specifying that's what a query means (different answer each
> time) or by including a "next pointer" in queries and replies.

The interface was implemented based on the knowledge that had been 
accumulated upto that point in time.  More time passes, we learn some 
things, we forget others.

I'll draft something,
Andrew