gevent 1.0 module name changed

importing gevent.coros raises warning as following:
```
>>> import kazoo.handlers.gevent
/usr/lib/python2.6/site-packages/kazoo/handlers/gevent.py:8: DeprecationWarning: gevent.coros has been renamed to gevent.lock
  import gevent.coros
```

Signed-off-by: Hiroaki KAWAI <kawai@stratosphere.co.jp>