Add functions PyUnicode_Append() and PyUnicode_AppendAndDel() that mirror
PyString_Concat() and PyString_ConcatAndDel() (the name PyUnicode_Concat()
was already taken).

Change PyObject_Repr() to always return a unicode object.

Update all repr implementations to return unicode objects.

Add a function PyObject_ReprStr8() that calls PyObject_Repr() and converts
the result to an 8bit string.

Use PyObject_ReprStr8() where using PyObject_Repr() can't be done
straightforward.
diff --git a/Objects/sliceobject.c b/Objects/sliceobject.c
index d56d69b..d526a07 100644
--- a/Objects/sliceobject.c
+++ b/Objects/sliceobject.c
@@ -19,7 +19,7 @@
 static PyObject *
 ellipsis_repr(PyObject *op)
 {
-	return PyString_FromString("Ellipsis");
+	return PyUnicode_FromString("Ellipsis");
 }
 
 static PyTypeObject PyEllipsis_Type = {
@@ -228,14 +228,14 @@
 {
 	PyObject *s, *comma;
 
-	s = PyString_FromString("slice(");
-	comma = PyString_FromString(", ");
-	PyString_ConcatAndDel(&s, PyObject_Repr(r->start));
-	PyString_Concat(&s, comma);
-	PyString_ConcatAndDel(&s, PyObject_Repr(r->stop));
-	PyString_Concat(&s, comma);
-	PyString_ConcatAndDel(&s, PyObject_Repr(r->step));
-	PyString_ConcatAndDel(&s, PyString_FromString(")"));
+	s = PyUnicode_FromString("slice(");
+	comma = PyUnicode_FromString(", ");
+	PyUnicode_AppendAndDel(&s, PyObject_Repr(r->start));
+	PyUnicode_Append(&s, comma);
+	PyUnicode_AppendAndDel(&s, PyObject_Repr(r->stop));
+	PyUnicode_Append(&s, comma);
+	PyUnicode_AppendAndDel(&s, PyObject_Repr(r->step));
+	PyUnicode_AppendAndDel(&s, PyUnicode_FromString(")"));
 	Py_DECREF(comma);
 	return s;
 }