_getField misses the cache when required field is in an array

[wildhart]

the _getField() function misses the cache when the field required is an array, e.g:

// user = {emails: [{address: '1@example.com', verified: true}, {address: '2@example.com', verified: false}]}

// this will miss the cache because _getField() cannot find the 'address' property 'emails'
Meteor.user("emails.address") 

I'm already working on a PR to fix this and a few other minor issues, should be available in a day or so...