BUG: only symmetrize matrix when it is not already symmetric
Merge pull request #4021 from jakevdp/fix_check_symmetric

BUG: only symmetrize matrix when it is not already symmetric
MAINT more informative assertion failure in test_common
Documentation of max depth parameter

Changed the docstring

Few docstring changes
Merge pull request #4026 from akshayah3/master

Documentation of max depth parameter in the DecisionTreeClassifier
change default to shuffle=True in SGDClassifier.
unhappy performance change in common tests.
also changed perceptron and passive agressive for consistency. fixed doctests, added whatsnew.