non-NDFFrame object error using pandas.SparseSeries.from_coo() function
There appears to be an issue with the .from_coo() sparse function. If the frame is viewed, it gives a "non-NDFFrame error". It could potentially be due to overlapping entries on the same index (this is handled in sparse.coo_matrix by adding the entries by default).

More details here: 
http://stackoverflow.com/questions/31970070/non-ndfframe-object-error-using-pandas-sparseseries-from-coo-function

Example:

```
import pandas as pd 
import scipy.sparse as ss 
import numpy as np 
row = (np.random.random(100)*100).astype(int) 
col = (np.random.random(100)*100).astype(int) 
val = np.random.random(100)*100 
sparse = ss.coo_matrix((val,(row,col)),shape=(100,100)) 
pd.SparseSeries.from_coo(sparse)
TypeError: cannot concatenate a non-NDFrame object
```
