message: fix(closure-compiler): remove internal flag from _isScalar
  the internal flag was causing issues with _isScalar checks when combined with closure compiler, removing it and opting for a comment and an obviously internal _name
diff: @@ -17,7 +17,7 @@ import { config } from './config';
  */
  export class Observable<T> implements Subscribable<T> {
  - /** @internal */
  + /** Internal implementation detail, do not use directly. */
  public _isScalar: boolean = false;
  protected source: Observable<any>;
  