combineAdd NotImplementedError for SparseDataFrame
[also, should probably be combine_add]

from pandas import DataFrame
df = DataFrame()
sdf = df.to_sparse()
sdf.combineAdd(DataFrame())

pandas\core\frame.pyc in combineAdd(self, other)
   3861         DataFrame
   3862         """
-> 3863         return self.add(other, fill_value=0.)
   3864
   3865     def combineMult(self, other):

pandas\core\frame.pyc in f(self, other, axis, level, fill_value)
    173     def f(self, other, axis=default_axis, level=None, fill_value=None):
    174         if isinstance(other, DataFrame):    # Another DataFrame
--> 175             return self._combine_frame(other, func, fill_value, level)
    176         elif isinstance(other, Series):
    177             return self._combine_series(other, func, fill_value, axis, level)

pandas\sparse\frame.pyc in _combine_frame(self, other, func, fill_value, level)
    414
    415         if fill_value is not None or level is not None:
--> 416             raise NotImplementedError
    417
    418         if not self and not other:

NotImplementedError:
