root testsuite: added resolve to the set of logging output.
Track aliases introduced in match arms like `(a, 1) | (a, 2) => ...`.

The goal: have a single NodeId that represents the set of multiple
occurrences of an identifier like `a` in the arm above.

To accomplish this, I:

  * Extended `middle::def::DefBinding` with `BindingAliasMode` to
    distinguish between the first occurrence of `a` (the
    representative) and the aliases that occur in the other disjuncts.
    Updated most clients to ignore the extra field.

  * Changed `middle::resolve` to track the representative for each
    binding's name and fill in the `BindingAliasMode` accordingly.

  * Changed `middle::mem_categorization` to use the representative of
    a binding when creating a `cmt` entry.

That small extra step was I think all that I needed to get `foo30.rs`
in the root testsuite working.
root testsuite: renamed files to reflect expectations about whether I should see warnings or not.