COSMIT refactor cross-validation strategies
Include LeavePLabelOut in refactoring
A further refactor
COSMIT Base class for KFold/StratifiedKFold validation
COSMIT make BaseKFold abstract
COSMIT Base class for [Stratified]ShuffleSplit
DOC fix docstring headings
ENH: removed leftover condition to get a wider application of the import all consistency check
FIX metrics/scoring bug with LeaveOneOut CV

Replace squeeze with ravel because the former can produce 0-d arrays:

>>> np.squeeze(np.array([True]))
array(True, dtype=bool)
>>> _.shape
()
MAINT remove deprecated gprime handling from FastICA + refactoring

Test coverage up from 88% to 99%.
COSMIT make helpers private with underscore
COSMIT make BaseKFold private with underscore
Merge pull request #2055 from jnothman/cv_refactor

[MRG] refactor partitioning cross-validation strategies
Enforce n_folds >= 2 for k-fold cross-validation
Use new-style format