When a scope contains no boxed variables, but the boxed variable compiler is being used, it may be a perf win to use a lighter-weight scope than DynamicScope. DynamicScope is already lazily allocating the variable array it contains, but it could be made lighter by eliminating all references used for variable management. This could make some method bodies with no captures variables faster to execute, since they'd have less per-call overhead. Also, as part of this fix, boxed variable scopes with no captured variables could skip the initialize-all-vars-to-nil for the DynamicScope they're using. This would eliminate that init cost for those methods.