title: scipy integrate.quad return an incorrect value
body: <p>i use scipy integrate.quad to calc cdf of normal distribution:</p>
  
  <pre><code>def nor(delta, mu, x):
      return 1 / (math.sqrt(2 * math.pi) * delta) * np.exp(-np.square(x - mu) / (2 * np.square(delta)))
  
  
  delta = 0.1
  mu = 0
  t = np.arange(4.0, 10.0, 1)
  nor_int = lambda t: integrate.quad(lambda x: nor(delta, mu, x), -np.inf, t)
  nor_int_vec = np.vectorize(nor_int)
  
  s = nor_int_vec(t)
  for i in zip(s[0],s[1]): 
      print i
  </code></pre>
  
  <p>while it print as follows:</p>
  
  <pre><code>(1.0000000000000002, 1.2506543424265854e-08)
  (1.9563704110140217e-11, 3.5403445591955275e-11)
  (1.0000000000001916, 1.2616577562700088e-08)
  (1.0842532749783998e-34, 1.9621183122960244e-34)
  (4.234531567162006e-09, 7.753407284370446e-09)
  (1.0000000000001334, 1.757986959115912e-10)
  </code></pre>
  
  <p>for some x, it return a value approximate to zero, it should be return 1. 
  can somebody tell me what is wrong?</p>