BUG: fixed reindex on a sparse block (was not taking correctly)

BUG: fixed sparse filling!!!!!

BUG: fixed pivot, need to define __hash__ to raise TypeError in NDFrame

BUG: downcast argument not in SparseBlock or sparse/frame.py for fillna
BUG: fix apply_reduce?

BUG: fixes in reduce.pyx to deal with reconstrucing a Series argument to the function
     if needed