Local commands broken by external dependencies in setup.py

When attempting to run local commands on a freshly created dexterity package (say for creating a new dexterity content type in the new package), I get the following error:

```
pkg_resources.DistributionNotFound: plone.namedfile[blobs]: Not Found for: my.package (did you run python setup.py develop?)
```

This generally happens because the named package is not currently available to Paste in the context of the current working set.

I'm not completely clear on how to deal with this. The dependency on plone.namedfile[blobs] is declared in the setup.py of the template. Is this a hard dependency for all dexterity content types? Is there some way we might remove this?

Read the generated package's setup.py and reproduce a local Paste command in a freshly created Dexterity package, checking the working set and the effect of running python setup.py develop. Determine whether plone.namedfile[blobs] is required for all generated content types or whether the template can avoid it, then verify that local commands no longer raise DistributionNotFound.

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