[cpp-threads] New strawman proposal

[Boehm, Hans]

I partially updated the strawman proposal accessible from

http://www.hpl.hp.com/personal/Hans_Boehm/c++mm

to reflect what I currently consider to be a more promising
approach to describing the memory model.  We no longer assume
that there is a total synchronization order, though we have the
leeway to introduce such a restriction for specific synchronization
primitives.  (And we clearly need to do so in some cases.)

I currently don't have much confidence in this.  Comments are
encouraged, as are patches to the document, comparisons
to other work, etc.

Note that the later sections of the document still need to be updated
for consistency with these revisions.  There is a comment telling you
where to stop reading.

Hans