title: Werkzeug-0.9.4 and python3_memcached-1.51 doesn't work on Python 3.4
body: <p>I'm using <code>werkzeug.contrib.cache.MemcachedCache</code> with python3_memcached-1.51 when I try to get\set data I get the following error: <code>memcache.MemcachedKeyTypeError: Key must be str()'s</code> here:
  <a href="https://github.com/eguven/python3-memcached/blob/master/memcache.py#L1039" rel="nofollow">https://github.com/eguven/python3-memcached/blob/master/memcache.py#L1039</a></p>
  
  <pre><code>if not isinstance(key, str):
      raise Client.MemcachedKeyTypeError("Key must be str()'s")
  </code></pre>
  
  <p>The key type is <code>bytes</code>, not <code>str</code>. So I checked deeper.</p>
  
  <p>Inside <code>werkzeug.contrib.cache.MemcachedCache</code> key is encoded into <code>bytes</code> (in Python3) like this:</p>
  
  <pre><code>if isinstance(key, text_type):
      key = key.encode('utf-8')
  </code></pre>
  
  <p><a href="https://github.com/mitsuhiko/werkzeug/blob/master/werkzeug/contrib/cache.py#L342" rel="nofollow">https://github.com/mitsuhiko/werkzeug/blob/master/werkzeug/contrib/cache.py#L342</a></p>
  
  <p>What is correct fix for this? Monkey patch?</p>