Changes

Summary

1. merged
2. proper build_master.build_uuid;
3. proper session_init *after* deleting db files (amending af6c493b0441);
4. clarified signature: more concise data;
5. tuned output;
6. more robust;
7. clarified signature: better default;
8. show only active builds;
9. clarified output;
10. tuned;
11. support for identified builds; more complete implementation of "isabelle build_worker";
12. clarified signature: more operations and options;
13. tuned;
14. clarified signature;
15. clarified signature;
16. more robust close() after failed initialization;
17. avoid repeated open_database_server: synchronized transaction_lock;
18. tuned signature;
19. more robust: proper transaction_lock;
20. tuned signature;
21. tuned signature;
22. tuned signature;
23. clarified signature: more options;
24. tuned;
25. clarified database for heaps: do not depend on build_database_test;
26. clarified signature;
27. tuned signature;