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 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.
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
Fix RFE n_features minimum value #3812 and make it simpler.
Merge pull request #3690 from queqichao/fix_bug_in_cross_validation_when_using_sparse_matrix_for_fit_params

+ Fix the bug of calling len when using sparse matrix for fit_params in ...
FIX clip SGD gradient on linear models for stability

The l2 weight decay rescaling is also kept positive (or null)
in case of strong regularization.
WEB fix css for new version of sphinx.