Backport New Scikit-Learn Validation Methods

[coveralls]

Pull Request Test Coverage Report for Build 138

• 110 of 164 (67.07%) changed or added relevant lines in 5 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-7.2%) to 87.85%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
sliced/externals/sklearn_partial.py	106	160	66.25%
<!--	Total:	110	164	67.07%	-->

Totals
Change from base Build 134:	-7.2%
Covered Lines:	564
Relevant Lines:	642

---

💛 - Coveralls