[PATCH]: Track tree that generated a MEM

[Richard Kenner]

I sent messages a long time ago thagt I was working on this and indeed sent
aqnd applied th0ousands of lins of patches in the first step.  This work
is not major enough to require a branch.

The remaining patches haven't been sent bevcause they haven't been finished:
the last month or so has been quite busy for me and I haven't gotten back to it
yet.  BUt I did send out a "roadmap", as I said.l  The idea is to make a new
data structure for MEM infomration and point the current field used for alis
at that.

I'm out of town now with bad access, so I'm sorry for this hard-to-read mjessage.