title: Set timezone to pandas dataframe
body: <p>Hi I'm trying to set the timezone to the dataframe and then changeit to UCT time zone.</p>
  
  <p>The data I'm reading is:</p>
  
  <pre><code>Date Time;G_h
  2012-03-31 23:00:00.000;0
  2012-03-31 23:15:00.000;0
  2012-03-31 23:30:00.000;0
  2012-03-31 23:45:00.000;0
  2012-04-01 00:00:00.000;0
  2012-04-01 00:15:00.000;0
  2012-04-01 00:30:00.000;0
  2012-04-01 00:45:00.000;0
  2012-04-01 01:00:00.000;0
  2012-04-01 01:15:00.000;0
  2012-04-01 01:30:00.000;0
  </code></pre>
  
  <p>I' use this code </p>
  
  <pre><code>df = pd.read_csv('input.csv', sep=";", index_col='Date Time', decimal=',')
  df.index = pd.to_datetime(df.index, unit='s')
  </code></pre>
  
  <p>My idea was to use this code:</p>
  
  <pre><code>df.index.tz_localize('Europe/Rome').tz_covert('UTC')
  </code></pre>
  
  <p>If I try to set the timezone <code>'Europe/Rome'</code> with this code </p>
  
  <pre><code>df.index=df.index.tz_localize('Europe/Rome')
  </code></pre>
  
  <p>I get this result:</p>
  
  <pre><code>Traceback (most recent call last):
    File "/usr/lib/python2.7/dist-packages/IPython/core/interactiveshell.py", line 2820, in run_code
      exec code_obj in self.user_global_ns, self.user_ns
    File "&lt;ipython-input-38-0aa69957bc90&gt;", line 1, in &lt;module&gt;
      d.index.tz_localize('Europe/Rome')
    File "/usr/local/lib/python2.7/dist-packages/pandas/tseries/index.py", line 1608, in tz_localize
      new_dates = tslib.tz_localize_to_utc(self.asi8, tz, infer_dst=infer_dst)
    File "tslib.pyx", line 1981, in pandas.tslib.tz_localize_to_utc (pandas/tslib.c:29912)
  AmbiguousTimeError: Cannot infer dst time from Timestamp('2012-10-28 02:00:00', tz=None), try using the 'infer_dst' argument
  </code></pre>
  
  <p>Any suggestion?</p>
  
  <p>I'm sure that the time is set correctly in the input file and the dst is ok!</p>