If a Meteor package had a file called index.js, the runtime module system
would resolve "meteor/<name>" to "/node_modules/meteor/<name>/index.js",
instead of falling back to Package[<name>] as expected.
Installing a stub for Package[<name>] at /node_modules/meteor/<name>.js
means the runtime module system no longer needs the fallback, and will no
longer be confused by index.js files.
Fixes#6590.
The npm install package has coevolved with the Meteor 1.3 module system,
and now it's time to prune off vestigial features that were never actually
useful to Meteor.
