title: history-search-backward with python-prompt-toolkit?
body: <p>In ipython 5+, readline behavior has changed significantly from previous versions.  Previously, I could type a partial command and press the keyboard up arrow to search backward through history for any command that started with those characters.  For example, if I had previously typed:</p>
  
  <pre><code>import blah
  import foo
  import foo
  </code></pre>
  
  <p>then typing <code>import ^</code> (with the carat representing up arrow) would cycle first through import foo, then import blah, with the cursor hovering over the <code>f</code> and the <code>b</code> respectively.  <code>import foo</code> would only show up once, i.e., the search was over unique entries.</p>
  
  <p>In ipython 5, the behavior is different, and I don't fully understand what it is doing, but it seems that only some of this behavior is retained.  The cursor position changes with each press of the up arrow, and searches are not over unique entries, but it seems that the first characters are still used to initiate the search.</p>
  
  <p>Is there any way to restore the gnu-readline-like history-search-backward functionality?</p>