Suggestion re tree-ssa merge

[Richard Kenner]

A tag should be placed on the tree just prior to the merge, so if people
want to be able to pick up the last pre-merge files, it should be easy to do
so.

Also, I think we need to make a decision on the 4.0 vs. 3.5 issue soon.
I feel very strongly that 4.0 is the appropriate choice because of the
significant change in behavior (for better or worse) of the compiler.