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.

Lib/sqlite3/test/userfunctions.py

@@ -198,7 +198,7 @@ class FunctionTests(unittest.TestCase):
         cur.execute("select returnblob()")
         val = cur.fetchone()[0]
         self.failUnlessEqual(type(val), bytes)
-        self.failUnlessEqual(val, memoryview(b"blob"))
+        self.failUnlessEqual(val, b"blob")
 
     def CheckFuncException(self):
         cur = self.con.cursor()