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/gdbmmodule.c b/Modules/gdbmmodule.c
index 5ee9c9a..86f98c0 100644
--- a/Modules/gdbmmodule.c
+++ b/Modules/gdbmmodule.c
@@ -251,14 +251,14 @@
 			"GDBM object has already been closed");
 	return -1;
     }
-    if (!PyBytes_Check(arg)) {
+    if (!PyString_Check(arg)) {
 	PyErr_Format(PyExc_TypeError,
 		     "gdbm key must be bytes, not %.100s",
 		     arg->ob_type->tp_name);
 	return -1;
     }
-    key.dptr = PyBytes_AsString(arg);
-    key.dsize = PyBytes_Size(arg);
+    key.dptr = PyString_AS_STRING(arg);
+    key.dsize = PyString_GET_SIZE(arg);
     return gdbm_exists(dp->di_dbm, key);
 }