SQLite locking and updates

[Dimitar Misev]

SQLite is locked for updates when a select or update is in progress.

rasdaman throws back a generic database error, but it should either

1. throw a meaningful error, e.g. database update failed because of query in progress
2. or it should queue the query and attempt the update a few times, until it succeeds or a timeout is reached.

I'd vote for option 2.