Summary
- merged
- back to compression in Isabelle/Scala (in contrast to f7174238b5e3), e.g. relevant for old_command_timings_blob, but also for prospective heaps;
- vacuum everything in the database;
- tuned;
- proper vacuum of session_info tables: only once per build process;
- tuned signature;
- more thorough database checks;
- more thorough treatment of build prefs, guarded by system option "build_through": avoid accidental rebuild of HOL etc.;
- clarified build options;
- clarified ML option vs. Scala option (see also caa182bdab7a);
- merge conflict
- unified function update and map update syntaxes