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/dictobject.c b/Objects/dictobject.c
index 1da24f4..b45a664 100644
--- a/Objects/dictobject.c
+++ b/Objects/dictobject.c
@@ -941,11 +941,11 @@
 
 	i = Py_ReprEnter((PyObject *)mp);
 	if (i != 0) {
-		return i > 0 ? PyString_FromString("{...}") : NULL;
+		return i > 0 ? PyUnicode_FromString("{...}") : NULL;
 	}
 
 	if (mp->ma_used == 0) {
-		result = PyString_FromString("{}");
+		result = PyUnicode_FromString("{}");
 		goto Done;
 	}
 
@@ -953,7 +953,7 @@
 	if (pieces == NULL)
 		goto Done;
 
-	colon = PyString_FromString(": ");
+	colon = PyUnicode_FromString(": ");
 	if (colon == NULL)
 		goto Done;
 
@@ -965,8 +965,8 @@
 		/* Prevent repr from deleting value during key format. */
 		Py_INCREF(value);
 		s = PyObject_Repr(key);
-		PyString_Concat(&s, colon);
-		PyString_ConcatAndDel(&s, PyObject_Repr(value));
+		PyUnicode_Append(&s, colon);
+		PyUnicode_AppendAndDel(&s, PyObject_Repr(value));
 		Py_DECREF(value);
 		if (s == NULL)
 			goto Done;
@@ -978,29 +978,29 @@
 
 	/* Add "{}" decorations to the first and last items. */
 	assert(PyList_GET_SIZE(pieces) > 0);
-	s = PyString_FromString("{");
+	s = PyUnicode_FromString("{");
 	if (s == NULL)
 		goto Done;
 	temp = PyList_GET_ITEM(pieces, 0);
-	PyString_ConcatAndDel(&s, temp);
+	PyUnicode_AppendAndDel(&s, temp);
 	PyList_SET_ITEM(pieces, 0, s);
 	if (s == NULL)
 		goto Done;
 
-	s = PyString_FromString("}");
+	s = PyUnicode_FromString("}");
 	if (s == NULL)
 		goto Done;
 	temp = PyList_GET_ITEM(pieces, PyList_GET_SIZE(pieces) - 1);
-	PyString_ConcatAndDel(&temp, s);
+	PyUnicode_AppendAndDel(&temp, s);
 	PyList_SET_ITEM(pieces, PyList_GET_SIZE(pieces) - 1, temp);
 	if (temp == NULL)
 		goto Done;
 
 	/* Paste them all together with ", " between. */
-	s = PyString_FromString(", ");
+	s = PyUnicode_FromString(", ");
 	if (s == NULL)
 		goto Done;
-	result = _PyString_Join(s, pieces);
+	result = PyUnicode_Join(s, pieces);
 	Py_DECREF(s);
 
 Done: