title: join omitting output lines when input sorted numerically
body: <p>i have two files, aa and bb:</p>
  
  <pre><code> $ cat aa 
  84 xxx
  85 xxx
  10101 sdf
  10301 23
  
   $ cat bb
  82 asd
  83 asf
  84 asdfasdf
  10101 22232
  10301 llll
  </code></pre>
  
  <p>i use the join command to join them:</p>
  
  <pre><code> $ join aa bb
  84 xxx asdfasdf
  </code></pre>
  
  <p>but what expected is 84, 10101 and 10301 all joined.
  Why only 84 has been joined?</p>