clarified signature: reduce boilerplate;

clarified messages;

tuned signature;

tuned structure;

clarified signature;

clarified signature;

clarified build process roles: "worker" vs. "build";

clarified database content; tuned signature;

tuned: prefer iterator.nextOption;

tuned whitespace and braces;

clarified signature: more uniform operations;

tuned signature: reduce boilerplate;

tuned signature;

proper clean_build of old data at start of new process --- allow to inspect remains of the last process;

more database content: formal end_build;

more operations;

clarified database content and prepare/init stages;

tuned signature;

tuned;

tuned;

less verbosity, amending 3bc49507bae5;

tuned comments; tuned structure;

tuned signature: avoid totally adhoc overriding;

separate static build_uuid from dynamic worker_uuid, to allow multiple worker processes participate in one build process;

enforce rebuild of Isabelle/ML, after various changes to build database management;

more detailed table "isabelle_build_serial": allow to monitor activity of build_process instances;

tuned output;

clarified database content: store actual value instead of index;

more robust: disallow override;

tuned messages;

more complete coverage of non-final Progress methods, notably for Server.Connection_Progress;

clarified signature: manage "verbose" flag via "progress";