title: Pandas plot function ignores timezone of timeseries
body: <p>When plotting a timeseries with the built-in plot function of pandas, it seems to ignore the timezone of my index: it always uses the UTC time for the x-axis. An example:</p>
  
  <pre><code>import numpy as np
  import matplotlib.pyplot as plt
  from pandas import rolling_mean, DataFrame, date_range
  
  rng = date_range('1/1/2011', periods=200, freq='S', tz="UTC")
  data = DataFrame(np.random.randn(len(rng), 3), index=rng, columns=['A', 'B', 'C'])
  data_cet = data.tz_convert("CET")
  
  # plot with data in UTC timezone
  fig, ax = plt.subplots()
  data[["A", "B"]].plot(ax=ax, grid=True)
  plt.show()
  
  # plot with data in CET timezone, but the x-axis remains the same as above
  fig, ax = plt.subplots()
  data_cet[["A", "B"]].plot(ax=ax, grid=True)
  plt.show()
  </code></pre>
  
  <p>The plot does not change, although the index has:</p>
  
  <pre><code>In [11]: data.index[0]
  Out[11]: &lt;Timestamp: 2011-01-01 00:00:00+0000 UTC, tz=UTC&gt;
  In [12]: data_cet.index[0]
  Out[12]: &lt;Timestamp: 2011-01-01 01:00:00+0100 CET, tz=CET&gt;
  </code></pre>
  
  <p>Should I file a bug, or do I miss something?</p>