[cpp-threads] Addition to strawman proposal

[Boehm, Hans]

I added a section to the beginning of

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

to explain why we are not just using the Java memory model.  After
thinking about this slightly more, I think there actually are some
pretty convincing arguments that the semantics of data races have to
stay undefined.

This arose in an off-line discussion with Bill.

Hans