title: Use integer64 as a key with data table
body: <p>I have a column of <code>integer64</code> and would like to use that as the key, only it does not work as shown below: the value gives <code>NA</code>.</p>
  
  <p><strong>This works</strong></p>
  
  <pre><code>s = data.table(id=1000000107000008595, value=10)
  setkey(s, id)
  s[J(1000000107000008595)]
  #             id value
  # 1: 1.00000e+18    10
  </code></pre>
  
  <p><strong>This does not work</strong></p>
  
  <pre><code>s = data.table(id=as.integer64(1000000107000008595), value=10)
  setkey(s, id)
  s[J(1000000107000008595)]
  #             id value
  # 1: 1.00000e+18    NA  # &lt;- NA is the problem
  </code></pre>