More Python 3 fixes

All doctests pass under both Python 2 and 3. Tested with debug builds of 3.4 and 2.7 and associated virtualenvs.

```
(py34d-venv) ~/workspace/pylibmc:py3k$ python --version
Python 3.4.0
(py34d-venv) ~/workspace/pylibmc:py3k$ nosetests
...........................
----------------------------------------------------------------------
Ran 27 tests in 23.080s

OK
```
```
(py27d-venv)~/workspace/pylibmc:py3k$ python --version
Python 2.7.6
(py27d-venv)~/workspace/pylibmc:py3k$ nosetests
............................
----------------------------------------------------------------------
Ran 28 tests in 22.143s

OK
```