Visitor refactoring: Step 1, couple (Env, vt<Env>) together in a tuple.
Fix linebreak and whitespace issues to placate make tidy.
auto merge of #7084 : pnkfelix/rust/fsk-visitor-refactoring, r=pnkfelix

This step 1 in my plan for issue #7081: Refactor visit.rs with a `@Visitor` trait.