Merging the py3k-pep3137 branch back into the py3k branch.
No detailed change log; just check out the change log for the py3k-pep3137
branch.  The most obvious changes:

  - str8 renamed to bytes (PyString at the C level);
  - bytes renamed to buffer (PyBytes at the C level);
  - PyString and PyUnicode are no longer compatible.

I.e. we now have an immutable bytes type and a mutable bytes type.

The behavior of PyString was modified quite a bit, to make it more
bytes-like.  Some changes are still on the to-do list.
diff --git a/Modules/socketmodule.c b/Modules/socketmodule.c
index 7fe562e..78aeb55 100644
--- a/Modules/socketmodule.c
+++ b/Modules/socketmodule.c
@@ -3659,8 +3659,8 @@
 		idna = PyObject_CallMethod(hobj, "encode", "s", "idna");
 		if (!idna)
 			return NULL;
-		assert(PyBytes_Check(idna));
-		hptr = PyBytes_AsString(idna);
+		assert(PyString_Check(idna));
+		hptr = PyString_AS_STRING(idna);
 	} else if (PyString_Check(hobj)) {
 		hptr = PyString_AsString(hobj);
 	} else {