Make null publication more performant

[dalgard]

With the FastRender package, all null publications are processed on every single request, including simple resource requests. This means that the publish function will be called many times before this.userId becomes available, so its performance can be improved a lot:

// roles_server.js
Meteor.publish(null, function () {
  if (this.userId) {
    return Meteor.users.find(this.userId, {
        fields: { roles: 1 }
      });
  }

  this.ready();
});

[alanning]

Just released v1.2.14, which changes the null pub to a named pub.