title: Matplotlib in tkinter can not exit
body: <p>I modified some matplotlib examples for test,this is code </p>
  
  <pre><code>#!/usr/bin/env python
  import matplotlib
  matplotlib.use('TkAgg')
  
  from matplotlib.backends.backend_tkagg import FigureCanvasTkAgg
  from matplotlib.figure import Figure
  import matplotlib.pyplot as plt
  
  import sys
  if sys.version_info[0] &lt; 3:
      import Tkinter as Tk
  else:
      import tkinter as Tk
  
  root = Tk.Tk()
  root.wm_title("test in TK")
  
  f = plt.figure(figsize=(3,3),dpi=98)
  
  labels = 'Frogs', 'Hogs', 'Dogs', 'Logs'
  sizes = [15, 30, 45, 10]
  colors = ['yellowgreen', 'gold', 'lightskyblue', 'lightcoral']
  explode = (0, 0.1, 0, 0) # only "explode" the 2nd slice (i.e. 'Hogs')
  
  plt.pie(sizes, explode=explode, labels=labels, colors=colors,
          autopct='%1.1f%%', shadow=True, startangle=90)
  
  plt.axis('equal')
  
  canvas = FigureCanvasTkAgg(f, master=root)
  canvas.show()
  canvas.get_tk_widget().pack(side=Tk.TOP, fill=Tk.BOTH, expand=1)
  canvas._tkcanvas.pack(side=Tk.TOP, fill=Tk.BOTH, expand=1)
  
  button = Tk.Button(master=root, text='Quit', command=sys.exit)
  button.pack(side=Tk.BOTTOM)
  
  Tk.mainloop()
  </code></pre>
  
  <p>I put a pie in tk,it can work,if I press 'Quit' button program will exit normally,if I press tk's 'X' the window will close,but this program in CMD window always waiting,not exit,I need use Ctrl+Break to close it,why?</p>