DOCS: Mistake in .cum* descriptions
For the .cum\* functions the generated documentation description is redundant. As an example, [DataFrame.cumsum()](http://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.cumsum.html?highlight=cumsum#pandas.DataFrame.cumsum) has the description "Return cumulative cumsum over requested axis." when it should say "Return cumulative sum over requested axis.". 

After looking into this, I found the problem on line 5507 of generic.py where the _name_ is being used instead of the _desc_. 
