title: scikit-lean GridSearchCV n_jobs != 1 freezing
body: <p>I'm running grid search on random forests and trying to use n_jobs different than one but the kernel freezes, there is no CPU usage. With n_jobs=1 it works fine. I can't even stop the command with ctl-C and have to restart the kernel.
  I'm running on windows 7. I saw that there is a similar problem with OS X but the solution is not relevant for windows 7.</p>
  
  <pre><code>from sklearn.ensemble import RandomForestClassifier
  rf_tfdidf = Pipeline([('vect',tfidf),
                    ('clf', RandomForestClassifier(n_estimators=50, 
  class_weight='balanced_subsample'))])
  
  param_grid = [{'vect__ngram_range':[(1,1)],
            'vect__stop_words': [stop],
            'vect__tokenizer':[tokenizer]
            }]
  if __name__ == '__main__':
  gs_rf_tfidf = GridSearchCV(rf_tfdidf, param_grid, scoring='accuracy', cv=5, 
                                                             verbose=10, 
                                                             n_jobs=2)
  gs_rf_tfidf.fit(X_train_part, y_train_part)
  </code></pre>
  
  <p>thanks.</p>