Should the --overload option (or, i like --sdk-path better) be something that is useful outside of debugging? Meaning is there a scenario in which we will need to ship the SDK with XPI? With a manifest's aliasing, I think we can get around this.

This could just be shorthand for adding the following to the manifest, copying the addon-sdk path into the alises:
```
  aliases: {
    'sdk/': './addon-sdk/sdk'
  }
```

If a use wants to ship WITH the SDK, what scenario would this be? Possibly overriding just one or two SDK modules? Can manually just add:
```
  aliases: {
    'sdk/tabs': './lib/tabs',
    'sdk/notifications': './lib/notifications'
  },
```

I do not think we have a use case for shipping the entire SDK inside of a XPI.