Interface implementations missing from schema with graphql-js 0.5.0

Hey.

First of all, thanks for this awesome library.

There's a breaking change in graphql-js v.0.5.0 that reads as follows:

• Types which implement an interface but are otherwise not referenced as a field return type are no longer automatically added to the Schema

It appears that it's now possible to pass types to include explicitly in the constructor of graphql.GraphQLSchema in index.js:

function Create (schema, implementation) {

  // ....

  // create an array of all types
  var all_types = Object.keys(object_types).map(function(typeName) {
    return object_types[typeName];
  });

  var schema = new graphql.GraphQLSchema({
    query: object_types['Query'],
    mutation: object_types['Mutation'],
    subscription: object_types['Subscription'],
    // and pass them here to include them in v.0.5.0 of graphql-js
    types: all_types
  });

  // .....
}

Adding all_types to the schema fixed our use case. I'm not sure whether this should be the default behaviour though.

Start in lib/index.js at Create and inspect how object_types are collected before graphql.GraphQLSchema is constructed. Check the graphql-js 0.5.0 schema behavior for interface implementations that are not field return types, then verify that the affected implementations are included in the resulting schema without breaking the existing query, mutation, or subscription setup.