performance tuning: avoid multiple db roundtrips;

clarified signature: more robust treatment of implicit state;

proper sync_database for Database_Progress consumer; more efficient (but less reactive) Database_Progress.stopped;

tuned message;

tuned;

tuned messages;

tuned signature: removed unused arguments;

minor performance tuning: avoid multiple db roundtrips;

more operations;

tuned;

limit size and complexity of bulk transactions;

more scalable write_entries and Export.consumer via db.execute_batch_statement;

clarified signature: filter batch;

more scalable write_messages via db.execute_batch_statement;

support for execute_batch: multiple statements in one round-trip;

more robust;

restrict input_messages to master build_process: avoid excessive db traffic for distributed build_workers;

more scalable Database_Progress via asynchronous Consumer_Thread.fork_bulk;

clarified main_loop: support timeout, which results in consume(Nil);

tuned;

clarified signature;

tuned signature;

tuned signature;

build_worker is stopped independently from master build_process;