Changes

Changes from Mercurial (hg http://isabelle.in.tum.de/repos/isabelle/ default)

Summary

1. merged
2. misc tuning and clarification: more standard Same.commit discipline;
3. tuned;
4. tuned names;
5. more operations; more accurate treatment of beta contraction in norm_term/norm_proof, following Envir.norm_term;
6. minor performance tuning: more careful treatment of empty environment;
7. clarified signature;
8. more zproofs;
9. clarified signature: support shared cache;
10. tuned;
11. tuned: avoid shadowing;
12. more zproofs;
13. tuned;
14. more operations; clarified cache;
15. tuned signature;
16. tuned names;
17. tuned -- eliminate clones;
18. tuned;
19. more operations;
20. more operations;
21. tuned;
22. clarified signature;
23. tuned;
24. tuned;
25. consider schedule calculation time in estimation;
26. compare previous build schedule with new one, to prevent regressions;