Changes

Summary

1. tuned comments;
2. more options;
3. removed obsolete "rsync" package;
4. tuned comments;
5. use "rsync --secluded-args" by default, discontinue obsolete option -P of sync tools;
6. tuned output;
7. misc tuning and clarification;
8. clarified output;
9. use remote copy of locally installed rsync component: for uniform version and options;
10. clarified signature: more abstract;
11. tuned signature;
12. more direct Hg_Sync.check_directory via SSH operations;
13. tuned;
14. clarified underlying SSH session of "isabelle hg_sync" and "isabelle sync";
15. clarified signature: avoid object-oriented "dispatch";
16. tuned;
17. clarified signature: more uniform Table() vs. Set();