No basic improvements branch for 3.5 - work on tree-ssa

[Richard Kenner]

    Why not just use the tree-ssa branch as the `basic improvements
    branch' for this round?  It has been regarded as 3.5-to-be for quite a
    while AFAIK.

Sort of, but that would put pressure on tree-ssa to actually make 3.5
or else cause a merge problem with the unrelated changes in that
branch.  I think it's much simpler for both efforts to not tie them
together like that in terms of schedules.