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/Python/modsupport.c b/Python/modsupport.c
index 8f25ed2..144fb4f 100644
--- a/Python/modsupport.c
+++ b/Python/modsupport.c
@@ -504,7 +504,7 @@
 					}
 					n = (Py_ssize_t)m;
 				}
-				v = PyBytes_FromStringAndSize(str, n);
+				v = PyString_FromStringAndSize(str, n);
 			}
 			return v;
 		}