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;