title: Drop consecutive duplicates from DataFrame with multiple columns and with string
body: <p>I have</p>
  <pre><code>df = pd.DataFrame([{'a':1,'b':1,'c':'x'},{'a':1,'b':1,'c':'x'}, {'a':2,'b':2, 'c':'x'}, {'a':1,'b':2,'c':'x'}, {'a':1,'b':1,'c':'x'}])
  
     a  b  c
  0  1  1  x
  1  1  1  x
  2  2  2  x
  3  1  2  x
  4  1  1  x
  </code></pre>
  <p>I'd like to drop consecutive duplicate rows only, i.e. only row at index 1</p>
  <pre><code>   a  b  c
  0  1  1  x
  2  2  2  x
  3  1  2  x
  4  1  1  x
  </code></pre>
  <p>I was about to do that with the following code, if column c isn't str</p>
  <pre><code>df[df[['c']].diff().ne(0).any(1)]
  </code></pre>
  <p>However, because column c is str, diff() doesn't work. What's the best way to achieve this?</p>