Pthreads patches

[Robert Collins]

I've still got 4 pthread patches from Thomas to review, but I've got to
go out for a while. 

**WARNING** I have code reviewed, but not regression tested these
changes. Thomas, could you merge your current sandbox with the latest
changes and ensure I haven't broken any of your patches ? Also, I've
probably caused the remaining patches to apply badly - if you have the
time, it would help me if you could regenerate the patches against CVS.

I should get the remaining code reviewed today sometime.

Rob