Fix/concat document definitions

[nhodges]

Issue Fixed apollographql#159

Proposed Changes

• Concatenate document definitions while filtering for duplicates

@daniellmb

Based on PR apollographql#105 by @evanrs, updated for current version of graphql-tag

Document fragments parsed by graphql-tag/loader lose their definitions when used with a gql tagged template literal. This is fixed by concatenating the document definitions—filtering for duplicates.

Without this, the following would fail:

import catFaceFragment from './catFaceFragment.gql';

const query = gql`
  query Kitten($name: String) {
    kitten(name: $name) {
      ... CatFace
    }
  }
  ${catFaceFragment}
`

#import "./whiskers.gql"

fragment CatFace on Cat {
  ... Whiskers
}

fragment Whiskers on Cat {
  whiskers {
    quantity
    length
    areWiderThanBody
  }  
}

Unknown fragment "Whiskers".