title: float64 with pandas to_csv
body: <p>I'm reading a CSV with float numbers like this:</p>
  
  <pre><code>Bob,0.085
  Alice,0.005
  </code></pre>
  
  <p>And import into a dataframe, and write this dataframe to a new place</p>
  
  <pre><code>df = pd.read_csv(orig)
  df.to_csv(pandasfile)
  </code></pre>
  
  <p>Now this <code>pandasfile</code> has:</p>
  
  <pre><code>Bob,0.085000000000000006
  Alice,0.0050000000000000001
  </code></pre>
  
  <p>What happen? maybe I have to cast to a different type like float32 or something? </p>
  
  <p>Im using <strong>pandas 0.9.0</strong> and <strong>numpy 1.6.2</strong>.</p>