title: poly1d gives erroneous coefficients when they are very large integers
body: <p>I am working with python 3.5.2 in ubuntu 16.04.2 LTS, and NumPy 1.12.1. When I use poly1d function to get the coeffs, there is a mistake with the computation:  </p>
  
  <pre><code>&gt;&gt;&gt; from numpy import poly1d
  &gt;&gt;&gt; from math import fabs
  &gt;&gt;&gt; pol = poly1d([2357888,459987,78123455],True)
  &gt;&gt;&gt;[int(x) for x in pol.coeffs]
  [1, -80941330, 221226728585581, -84732529566356586496]
  </code></pre>
  
  <p>as you see in this list the last element is not correct. When I build the polynomial using Wolfram Alpha, I get:</p>
  
  <pre><code>x^3 - 80941330 x^2 + 221226728585581 x - 84732529566356580480
  </code></pre>
  
  <p>The last coefficient is different using poly1d (the first-one ends in ...496 and the other ends in ...480).Ii have to suppose that the correct ones is the last compute (made by WolframAlpha).</p>
  
  <p>Is this a bug or is there something I am not taking account of? I've probed with roots with low absolute value; and in this case the computation is correct. But when I use "big roots", the difference is notable. </p>