title: Seaborn : linear regression on top of a boxplot
body: <p>With seaborn, how I can use sns.boxplot and sns.lmplot to obtain a boxplot with a regression line from the same data ? 
  This does not work : </p>
  
  <pre><code>tips = sns.load_dataset("tips")
  ax = sns.boxplot(x="size", y="tip", data=df)
  ax = sns.lmplot(x="size", y="tip", data=tips, x_estimator=np.mean); 
  </code></pre>