The metabucket expects vectors, not scalars. This causes the value
to be inaccessible when loaded by the ProcessManager for rating,
because it uses the Bucket implementation expecting vectors.
This wasn't noticed at first because it works through TAME's map.
* doc/bucket.texi (Metabucket): Clarify expected data format.
* src/server/db/MongoServerDao.js (saveQuote): Store
`meta.liza_timestamp_initial_rated' as a vector.