Patch for errors introduced in the sparse label binarizer

The error:

```
======================================================================
ERROR: Test that ovr works with classes that are always present or absent
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Traceback (most recent call last):
  File "/home/travis/anaconda/envs/testenv/lib/python2.6/site-packages/nose/case.py", line 197, in runTest
    self.test(*self.arg)
  File "/home/travis/build/scikit-learn/scikit-learn/sklearn/tests/test_multiclass.py", line 73, in test_ovr_always_present
    assert_warns(UserWarning, ovr.fit, X, y)
  File "/home/travis/build/scikit-learn/scikit-learn/sklearn/utils/testing.py", line 135, in assert_warns
    result = func(*args, **kw)
  File "/home/travis/build/scikit-learn/scikit-learn/sklearn/multiclass.py", line 202, in fit
    n_jobs=self.n_jobs)
  File "/home/travis/build/scikit-learn/scikit-learn/sklearn/multiclass.py", line 92, in fit_ovr
    for i in range(Y.shape[1]))
  File "/home/travis/build/scikit-learn/scikit-learn/sklearn/externals/joblib/parallel.py", line 644, in __call__
    self.dispatch(function, args, kwargs)
  File "/home/travis/build/scikit-learn/scikit-learn/sklearn/externals/joblib/parallel.py", line 391, in dispatch
    job = ImmediateApply(func, args, kwargs)
  File "/home/travis/build/scikit-learn/scikit-learn/sklearn/externals/joblib/parallel.py", line 129, in __init__
    self.results = func(*args, **kwargs)
  File "/home/travis/build/scikit-learn/scikit-learn/sklearn/multiclass.py", line 57, in _fit_binary
    str(classes[c]))
TypeError: list indices must be integers, not numpy.float64
----------------------------------------------------------------------
```