[MRG] Let OneVsOneClassifier use list of targets

Fix for #3863 
Can you please run [pep8](https://pypi.python.org/pypi/pep8) or [flake8](https://pypi.python.org/pypi/flake8) on the file you changed in this PR and fix the error / warnings that pertains to the lines of your change?

In particular, don't use more than 79 columns on a source code line.