TODOs:
* File::reopen_with_fdflags is unimplemented, File::get_fdflags is lying - these are
  fcntl on unix, reopenfile / require reopening on windows.



# Linux

* path_link
    - need DirExt::hard_link that follows symlinks.
* path_rename_trailing_slashes
    - trailing slash behavior of files is wrong: trailing slashes are ignored,
      should cause an error.
* remove_directory_trailing_slashes
    - cap-std Dir::remove_dir gives EINVAL when trying to remove dir with
      trailing slash. otherwise, everything passes.

* fd_flags_set
    - set_fdflags is not implemented. test wanted to clear O_APPEND mode
* path_filestat
    - fdstat.fs_flags is not populated correctly - APPEND | SYNC aren't
      present because File::get_fdflags isnt implemented correctly


# Windows

fd_readdir
file_allocate
interesting_paths
nofollow_errors
path_rename

path_link

path_rename_trailing_slashes
path_symlink_trailing_slashes
remove_directory_trailing_slashes
unlink_file_trailing_slashes

fd_flags_set
path_filestat