DS.findAll wasn't added to completedQueries

[chieffancypants]

Hi there, back again with a similar issue to #90. There may be more of these, but just opening tickets as I encounter them. Figured this time I'd help resolve it

DS.findAll caches all objects properly, but DS.find() doesn't pull from the cache and instead triggers a new XHR:

DS.findAll('document').then(function (documents) {
    DS.get('document', documents[0].id)  // pulls from cache properly
    DS.find('document', documents[0].id) // triggers another XHR for the same document already in the cache
  });