[MRG] Support unseen labels LabelBinarizer and test (Backward compatibility)

Patches the updates to LabelBinarizer for sparse support which broke the case the case with unseen labels. For issue #3462
Can you please add a check with:

```
lb.fit_transform(['b', 'd', 'e'])
```
and then check:

```
lb.transform(['a', 'b', 'c', 'e', 'f'])
```

to cover more possible ordering-related issues?