Remove unecessary retain/release dance of URL
Introduce the concept of a record's contents not being complete

For directories to know there may be more contents yet to come. When
not complete, the tick mark is not drawn
Mark a record's content as complete affects all descendants
Mark root transfer record as complete once uploader has been invalidated
Merge pull request #68 from karelia/contents-complete

Don't consider directory transfer records to be finished until their contents are complete
Merge branch 'v2.x-beta' into uploader-urls