Dataframe.ix behavior inconsistent (depends on index type)
I would expect that ix[n] would return the n-th row in a data frame (doc is missing so I'm not sure). This seems to work as such with an index that is not integer based (say dates). But it fails with an int-based index that is not a continuous range starting at 0 (and there is no reason it should).
Example with date index:
    dates = np.asarray(date_range('1/1/2000', periods=8))
    d = DataFrame(randn(8, 4), index=dates, columns=['A', 'B', 'C', 'D'])
    d.ix[1]

returns the second row correctly.
Example with int index:
    numbers = range(4,12)
    n = DataFrame(randn(8, 4), index=numbers, columns=['A', 'B', 'C', 'D'])
    n.ix[1]

Returns a key error. A bug, or so it seems. 
