Release 3.0: DB->sync and DB->close

In previous Berkeley DB releases, the DB->close() and DB->sync() methods discarded any return of DB_INCOMPLETE from the underlying buffer pool interfaces, and returned success to its caller. (The DB_INCOMPLETE error will be returned if the buffer pool functions are unable to flush all of the database's dirty blocks from the pool. This often happens if another thread is reading or writing the database's pages in the pool.)

In the 3.X release, DB->sync() and DB->close() will return DB_INCOMPLETE to the application. The best solution is to not call DB->sync() with the DB_NOSYNC flag to the DB->close() method when multiple threads are expected to be accessing the database. Alternatively, the caller can ignore any error return of DB_INCOMPLETE.