+ 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
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.
MAINT refactor gradient boosting code

Fixes gh-3790
TST update numerical overflow (non-regression) tests
Fixes #3644
Added NRT for return_path propagation check
DOC: Fix LabelBinarizer docstring to rst format bug

- Also add line to make multilabel classification example more instructive
- Use one line for 2D array so syntax highlighting is correct
Merge pull request #3883 from ogrisel/sgd-stability

Improve stability of SGDClassifier / SGDRegressor with gradient clipping
DOC update whats_new.rst for SGD stability
FIX unlikely pickling error of splitters
TST add a toy test for min_weight_samples_leaf
Merge pull request #3823 from ragv/omp-3644

[MRG+1] Fixes #3644
Typo
ENH add coverage multilabel ranking metric
Remove copy paste mistake
DOC improve documentation of coverage
TST make separate tests for coverage + remove redundant tests with commons