COSMIT removed unused imports, fixed error message in test of boosting
ENH break ties in OvO using scores
TST test for breaking OVO ties
test case for unfitted idf vector
raise ValueError for unfitted idf vector

Catches an obscure AttributeError raised by calling .transform on a TfidfTransformer (with use_idf=True) that has not learned an idf vector.
Merge pull request #1656 from rlmv/idf_diag

Fix AttributeError caused by an unlearned idf vector
Remove compute_importances parameter
What's new
FIX docstring deletions
ADD test coverage for _check_stop_list
FIX comment typo
ADD test cases to fill out VectorizerMixin coverage
ADD another VectorizerMixin test
ADD test for get_feature_names
ADD test for tfidf fit with incompatible n_features
ADD test for TfidfVectorizer attribute setters
ENH: Remove compute_importances in AdaBoost
ENH: Update feature_importances in GBRT
ENH: remove "mse" method and simplify
COSMIT