Auto-run the Task that is returned from Task.run

[cpettitt]

This has been raised as a surprise by several people - most recently by @jhartman. The behavior of ParSeq differs between core ParSeq, Play, and Restli. ParSeq and Play require Tasks to be explicitly run. Restli auto-runs the returned Task.

In an environment where users are using seq / par, the auto-run behavior is most intuitive. In an environment where users are using context.after, the opposite is true. Here's an example where auto-run would do the wrong thing:

    final Task<String> parent = new BaseTask<String>()
    {
      @Override
      protected Promise<? extends String> run(final Context context) throws Exception
      {
        context.after(a).run(b);
        context.after(a).run(c);
        context.after(b, c).run(d);
        context.run(a);
        return d;
      }
    };

With auto run we'd try to run d before b and c. However, context.after is intended as a low-level construct for building up more user friendly tasks, such as the above mentioned seq and par, so it seems better to make run handling special for context.after and not the other way around.