adding support for class_weight in fit method
adding warning if passing class_weight through fit
changing warn message, making it Deprecation Warning, and removing negative index for py2.7
adding simplefilter for warning
changing warning test to use assert_raises_message
ENH: Use check_X_y in pairwise_distances_argmin
Merge pull request #3962 from MechCoder/check_X_y

[MRG] ENH: Use check_X_y in pairwise_distances_argmin
Merge pull request #3931 from dsullivan7/cwwarn

[MRG+1] raising warning for class_weight in fit method
Added feature to fix #1523
ENH decision_function now returns #votes and scaled scores.
TST Added test to assertain correlation of decision function and prediction
FIX Implemented _check_is_fitted for OvO similar to the one for OvR
FIX Correct and separate the scaling logic for scores
TST Add decision_function tests to check for votes/scores

ovo_ties test will use decision function to calculate votes and score.
COSMIT Undo aggressive pep8
ENH use the decision_function to compute the prediction