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/methodobject.c b/Objects/methodobject.c
index 4204db7..6199805 100644
--- a/Objects/methodobject.c
+++ b/Objects/methodobject.c
@@ -184,9 +184,9 @@
 meth_repr(PyCFunctionObject *m)
 {
 	if (m->m_self == NULL)
-		return PyString_FromFormat("<built-in function %s>",
+		return PyUnicode_FromFormat("<built-in function %s>",
 					   m->m_ml->ml_name);
-	return PyString_FromFormat("<built-in method %s of %s object at %p>",
+	return PyUnicode_FromFormat("<built-in method %s of %s object at %p>",
 				   m->m_ml->ml_name,
 				   m->m_self->ob_type->tp_name,
 				   m->m_self);