[RFC] allocator reorg

[Loren James Rittle]

> This patch adds the MT allocator graciously donated by Stefan Olsson and
> Ola Rönnerup. It also re-organizes the allocator code to improve
> legibility and to make it more modular.

I like what you did far better than any meek tweaking I was going to
do.  I have reviewed it and support the new style.  I think most/all
of the issues raised over the months have been addressed. - Loren