tests/test-gendoc-ru.t

rust-cpython: rename PyLeakedRef to PyLeaked

This series will make PyLeaked* behave more like a Python iterator, which
means mutation of the owner object will be allowed and the leaked reference
(i.e. the iterator) will be invalidated instead.

I'll add PyLeakedRef/PyLeakedRefMut structs which will represent a "borrowed"
state, and prevent the underlying value from being mutably borrowed while the
leaked reference is in use:

  let shared = self.inner_shared(py);
  let leaked = shared.leak_immutable();
  {
      let leaked_ref: PyLeakedRef<_> = leaked.borrow(py);
      shared.borrow_mut();  // panics since the underlying value is borrowed
  }
  shared.borrow_mut();  // allowed

The relation between PyLeaked* structs is quite similar to RefCell/Ref/RefMut,
but the implementation can't be reused because the borrowing state will have
to be shared across objects having no lifetime relation.

PyLeaked isn't named as PyLeakedCell since it isn't actually a cell in that
leaked.borrow_mut() will require &mut self.

#require docutils gettext

  $ $TESTDIR/check-gendoc ru
  checking for parse errors