title: mask_missing is not defined in pandas.core.common?
body: <p>Recently I installed zipline with Anaconda, together with it is pandas 0.18.1. When I tried to import zipline, it reports following error:</p>
  
  <blockquote>
    <p>C:\Anaconda3\envs\helloworld\lib\site-packages\zipline\utils\munge.py in &lt;module&gt;()</p>
    
    <p>13 # See the License for the specific language governing permissions and</p>
    
    <p>14 # limitations under the License.</p>
    
    <p>---> 15 from pandas.core.common import mask_missing</p>
    
    <p>16 try:</p>
    
    <p>17     from pandas.core.common import backfill_2d, pad_2d</p>
    
    <p>ImportError: cannot import name 'mask_missing'</p>
  </blockquote>
  
  <p>Then I checked Pandas pandas.core.common.py source code, mask_missing is not defined there. May I know which version of Pandas we should use? </p>
  
  <hr>
  
  <p>I found this online: <a href="http://nullege.com/codes/show/src%40p%40a%40pandas-0.13.1%40pandas%40core%40generic.py/53/pandas.core.common.mask_missing/python" rel="nofollow">http://nullege.com/codes/show/src%40p%40a%40pandas-0.13.1%40pandas%40core%40generic.py/53/pandas.core.common.mask_missing/python</a></p>
  
  <p>It seems like in pandas 0.13 mask_missing is still there. I will downgrade pandas to 0.13 first and see if it solves problem</p>