The version of the update function is chosen depending on the URI that is
passed to the update method of the repo module:
An ID URI: the ___worker_update_from_ids is selected, the user will be able
to queue the different kara to download by calling again the update method
with others ID URI
Anything else: the ___worker_update is selected. It will download all the
database from Kurisu, filtering if the passed URI is not URI_NULL.
The aim here is to offer a download process option which permit the user of
doing a simple dry-update and then selecting the different karas he wants to
download id per id.
