title: specify the time zone for pandas to_datetime function
body: <p>When I use the pd.to_datetime function on the data as shown below I get I time zone aware series that is in UTC. I am aware of the tz_convert function but I do not believe it suits my purpose.</p>
  <p>The times that I have are in the US central time zone. If I don't specify this then my 21:00 CDT is assumed to be 21:00 UTC and tz_convert would incorrectly give me 16:00-5:00. Maybe I am just confused by this representation of time but as I understand it this would incorrectly represent 21:00 CDT as 16:00 CDT.</p>
  <p>If I could specify the time zone to use when converting the time column I do not feel this would be an issue. Or if there was simply a way to set the timezone without doing a conversion. Below is an example:</p>
  <pre><code>df = pd.DataFrame([])
  theseAreCentralTime = ['2015-04-24T23:48:28Z','2015-04-24T23:40:59Z','2015-04-24T23:48:28Z']
  df['time'] = theseAreCentralTime
  df['time'] = pd.to_datetime(df['time'])
  print(df['time'].dt.tz)
  print(df['time'])
  df['time'] = df['time'].dt.tz_convert('US/Central')
  print(df['time'].dt.tz)
  print(df['time'])
  </code></pre>
  <p>the output of this is:</p>
  <pre><code>UTC
  0   2015-04-24 23:48:28+00:00
  1   2015-04-24 23:40:59+00:00
  2   2015-04-24 23:48:28+00:00
  Name: time, dtype: datetime64[ns, UTC]
  US/Central
  0   2015-04-24 18:48:28-05:00
  1   2015-04-24 18:40:59-05:00
  2   2015-04-24 18:48:28-05:00
  Name: time, dtype: datetime64[ns, US/Central]
  </code></pre>
  <p>I am hoping to see the times as:</p>
  <pre><code>23:48:28-05:00 
  23:40:59-05:00
  23:48:28-05:00
  
  etc
  </code></pre>
  <p>Thanks in advance for any help</p>