title: How to convert datetime.time columns in dataframe to string
body: <p>I've been struggling to convert two columns in a pandas.
  The frame contains many columns, and 2 columns with dates: 'datelog'(is a date) and 'Timeofday' (is a time).
  The column datelog is a string.
  The column  Timeofday is  a datetime.time() format.
  The dateframe display is as folows:</p>
  
  <pre><code>     datelog Timeofday
  0  30-APR-15  14:15:43
  1  30-APR-15  14:16:13
  2  30-APR-15  14:16:43
  3  30-APR-15  14:17:13
  4  30-APR-15  14:17:43
  5  30-APR-15  14:18:13
  6  30-APR-15  14:18:43
  7  30-APR-15  14:19:13
  8  30-APR-15  14:19:43
  9  30-APR-15  14:20:13
  </code></pre>
  
  <p>My goal is to concatenate these two column to use them as a index for a timeseries. Can somebody point me in the right direction?</p>