libotutil: Add API to create directory hierarchy recursively *and* fsync

To be really sure that any directory entries have hit disk we need to
call fsync() on the directory fd.  This API allows us to conveniently
create a directory hierarchy, fsyncing all of it along the way.

src/libotutil/ot-gio-utils.h

@@ -83,5 +83,13 @@ gboolean ot_gfile_atomic_symlink_swap (GFile          *path,
                                        GCancellable   *cancellable,
                                        GError        **error);
 
+gboolean ot_util_ensure_directory_and_fsync (GFile         *dir,
+                                             GCancellable  *cancellable,
+                                             GError       **error);
+
+gboolean ot_util_fsync_directory (GFile         *dir,
+                                  GCancellable  *cancellable,
+                                  GError       **error);
+
 G_END_DECLS