Added a unit test to ensure that there are no spurious repeating values in the thresholds returned by roc_curve because of machine precision, and a quick stab at a fix.
Slightly expanded the docstring for the test_roc_nonrepeating_thresholds test. Added named slice variables to same, for readability.
Improved the treatment of the machine precision issue for calculating ROC thresholds. Added a comment explaining why the treatment is needed.
Minor refactoring of the repeated-roc-thresholds test, for clarity.
Added a backport of numpy.isclose from numpy v1.8.1. This function was not available until numpy v1.7
Changed metrics.py to use the new backward-compatible version of np.isclose
PEP8 fix
Merge pull request #3268 from jblackburne/nonrepeating_roc_thresholds

[MRG+2] Nonrepeating ROC thresholds