require twisted 13.1.0, since 13.2.0 broke backward compatible

I got this error with 13.2.0
````
root@integration:/etc/nagios/nrpe.d# service carbon-cache-0 start
Traceback (most recent call last):
  File "/usr/local/graphite/bin/carbon-cache.py", line 28, in <module>
    from carbon.util import run_twistd_plugin
  File "/usr/local/graphite/local/lib/python2.7/site-packages/carbon/util.py", line 21, in <module>
    from twisted.scripts._twistd_unix import daemonize
ImportError: cannot import name daemonize

````

Switched to 13.1.0, it worked normal.