Make the constructor property of td.replaced() instantiable types useful

[searls]

Right now if you use td.replace on an instantiable function, what gets returned includes a constructor property, but it's not actually able to be used to stub/verify calls to new Thing() in the subject.

This was an oversight on my part because I hadn't thought of it, and I'm not quite sure what to do about it.

h/t @appleton via twitter

[alexblom]

This would be really useful for me. In my case, I'm creating non-external objects with new Object({params}), and where passing the correct params is very important. I'm unsure how to test this behaviour with testdouble today.

As an example, in a larger function you will see:

    validatePlugin = new ValidatePluginTask({
      project: this.project,
      ui: this.ui,
      platform: platform,
      pluginName: 'cordova-plugin-whitelist'
    });

I really care that nobody forgot to pass pluginName, and that value of pluginName matches expectations.

[searls]

Right on @alexblom -- I think this is important as well, and you have a very valid point. Unfortunately, I'm slammed with talk prep and travel the next month or two and don't want to commit to doing this myself soon.

[searls]

This will be fixed as an acceptance criteria of #166, so I'm closing it here