setex only accepts Integers.

```python
>>> r = redis.Redis(db=1)
>>> r.setex('foo', 'bar', 1.2)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/sdehaan/Documents/Repositories/vumi/ve/lib/python2.7/site-packages/redis/client.py", line 1384, in setex
    return self.execute_command('SETEX', name, time, value)
  File "/Users/sdehaan/Documents/Repositories/vumi/ve/lib/python2.7/site-packages/redis/client.py", line 361, in execute_command
    return self.parse_response(connection, command_name, **options)
  File "/Users/sdehaan/Documents/Repositories/vumi/ve/lib/python2.7/site-packages/redis/client.py", line 371, in parse_response
    response = connection.read_response()
  File "/Users/sdehaan/Documents/Repositories/vumi/ve/lib/python2.7/site-packages/redis/connection.py", line 311, in read_response
    raise response
redis.exceptions.ResponseError: value is not an integer or out of range
```