tracker-utilities: Ignore XDG use dirs set to $HOME
If the "index-recursive-directory" key lists an XDG user dir which is set to $HOME (e.g., in my case, I have no Desktop folder), then we assume the whole home dir is recursively indexed. As a result, we show stars everywhere under the home dir. But this is not what Tracker's files miner does. It ignores these cases, avoiding recursively indexing the whole home dir. So, skip these cases. Also, document the utility function.