ENH add sparse parameter to OneHotEncoder
DOC: note about numerical precision in euclidean_distances

Fixes #2914.
TST fix failing doctest for OneHotEncoder
FIX GBRT missing from covertype benchmark usage
DOC: Update dead link in cross_decomposition.rst
Merge pull request #2917 from ariddell/patch-1

DOC: Update dead link in cross_decomposition.rst
MAINT drop support for NumPy < 1.6.1
MAINT drop support for SciPy < 0.9

TODO: get rid of solve_triangular. Just replacing it by scipy.linalg's
breaks OMP and least-angle regression.
TST: test utils.extmath more robust