Denormalizing nested fields trigger unwanted updates when other part of the nested field is modified

[vparpoil]

If one collection is referencing nested fields as such :

Task.cache({
    type: 'one',
    collection: Meteor.users,
    fields: ['profile.firstName', 'profile.lastName'],
    referenceField: 'userId',
    cacheField: 'userCache'
})

Then an update of the profile will trigger unwanted cascading updates that could result in poor application performance depending on collection sizes :

Meteor.users.update({_id: "some id"}, { '$set': { 'profile.connexionDate': new Date() } })

I will try to work on a PR to fix this. Any hints on a proper way to treat this issue will be appreciated