FIX PLSRegression again supports 1d target

Fixes plot_compare_cross_decomposition example
+ Fix the bug of calling len when using sparse matrix for fit_params in cross_validation.py.
+ Fix the bug of calling len when using sparse matrix for fit_params in cross_validation.py.
+ Add test case for the above fix.
Merge branch 'fix_bug_in_cross_validation_when_using_sparse_matrix_for_fit_params' of https://github.com/queqichao/scikit-learn into fix_bug_in_cross_validation_when_using_sparse_matrix_for_fit_params

Conflicts:
	sklearn/cross_validation.py
FIX in KDE fit and score allow y=None, add test for use with pipeline and gridsearch
Fix RFE n_features minimum value #3812
Accelerate AffinityPropagation.

Accelerate AffinityPropagation for large inputs using standard tricks
(in-place operations and out parameters) to avoid extra allocations.

Basic tests on datasets for 1000 points in 2D show ~10-20% increase in
speed.
Merge pull request #3826 from amueller/kde_y_none

[MRG+1] FIX in KDE fit and score allow y=None
Add random forests to document classification example.
Minor typo in plot_dict_face_patches.py
FIX: Raise error when patch width/height is greater than image width/height
Update documentation.rst

Update documentation header. See #3827.
AffinityPropagation: save memory by reusing tmp.
added n_init check for k_means()
Merge pull request #3871 from anntzer/fast-affinity-propagation

[MRG+2] Accelerate AffinityPropagation.
DOC fix what's new for sparse trees
Merge pull request #3858 from banilo/km_init

k-means: add n_init argument check
MAINT bump joblib to 0.8.4

This includes a fix for #3835 (under Python 3.3+ only).
DOC add documentation improvements to what's new
DOC update whats_new.rst for AffinityPropagation optim