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
ENH Added method_filter to all_estimators function.

method_filter can be used to filter the estimators based on the existence of one or more methods passed as a list of method names.

The default method_filter value is None.

It can also be an empty list.
FIX fix the removal of set while resolving merge conflicts

COSMIT minor pep8 fixes in sklearn.utils.testing
TST Added partial_fit estimator checks

* Test for estimator restart upon fit
* Validation of classes argument
* Test to check that partial_fit returns reference to self
* Refactor multiple imports from utils.testing into single import
TST Added tests for estimators implementing partial_fit
ENH method_filter will now accept string or list of strings

ENH method_filter/type_filter allows prefixing filter names with !
    to skip those particular methods/types.

ENH type_filter will skip if the list is empty

COSMIT minor cosmetic and pep8 fixes
TST Added tests for all_estimators function