Changes

Summary

1. merged
2. prefer statically-typed close operation, avoid Java 11 warning: "Illegal reflective access by scala.reflect.package$ to method sun.net.httpserver.LeftOverInputStream.close()";
3. more robust hostname for Isabelle cronjobs: do not rely on target OS installation for resulting build_log database content;
4. more uniform wrt. File.find_files;
5. proper use of stat() vs. lstat() (for symlinks);
6. more uniform find_files, notably for symlinks;
7. is_file/is_dir/read_dir: more uniform treatment of errors and boundary cases, notably for symlinks in ssh;
8. clarified default (amending 72a9860f8602): avoid implicit change of File.find_files (it can have bad effects e.g. on "isabelle update_cartouches");
9. fixed import
10. extract example for ab_group_add_on_with
11. generalized local_typedef_ab_group_add
12. use locales in Group_On_With