This will be necessary to "tag" the default suggested collection to
which imported items are added, so that one may detect whether it
already exists.

The default collection during import is named based on the timestamp
of the items being imported. The user-visible representation of the
timestamp depends on the locale, and can't be relied upon for
identification. Therefore, the raw timestamp is added to the
nao:identifier as:
  photos:collection:local:<timestamp>

#29