109.52.00

- Changed `Pipe.iter_without_pushback` to never call `f` after
  `Pipe.close_read` has been called.

  The new behavior is like `Pipe.iter`.

  Changed the implementation of `Pipe.fold_gen` and `Pipe.transfer_gen`
  to be analogous to `Pipe.iter_without_pushback`, and in particular to
  process as many elements as possible before calling `values_available`.