fix-761: do not ignore devDeps that are included as in prod pkg (#761)

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Summary

When installing with production flag the devDeps also follow the flow, but are set to ignored. Chances are that a production dependency can be smartly resolved and shared with a devDep. If this is the case make sure this package also gets set to USED when being included, so it won't be ignored later.

This solves at least:

• yarn install --production doesn't install correct dependencies #761
• Some dependencies don't get installed if they're shared between a regular and a devDependency #1014

Test plan

npm run test should not give errors and contain a new use-case for these cases.

Extracted & tested use-case from the issue:

$ git clone https://github.com/donovan-graham/yarn-example-app.git
$ cd yarn-example-app

Should resolve and give the correct dependencies:

$ yarn install --production
$ yarn check --production
$ yarn check --production --integrity
$ npm run start

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Closing in favour for possible better solutions. More (other) issues are related as-well to inheriting and propagating visibility.