Changes

Summary

1. merged
2. proper build_selection for clean_build (amending 961285f581e6): e.g. relevant for "isabelle build_doc";
3. clarified signature (again);
4. clarified exclusion: operate on completed selection, as last step;
5. tuned;
6. tuned signature;
7. clarifified selection: always wrt. build_graph structure; tuned signature;
8. tuned;
9. tuned signature;