title: Error when importing mock.call if doctest are enabled
body: <p>When I have <em>doctest</em> enabled and import <code>call</code> I get this exception:</p>
  
  <pre class="lang-py prettyprint-override"><code>/usr/lib/python3.6/doctest.py:933: in find
      self._find(tests, obj, name, module, source_lines, globs, {})
  /usr/lib/python3.6/doctest.py:992: in _find
      if ((inspect.isroutine(inspect.unwrap(val))
  /usr/lib/python3.6/inspect.py:516: in unwrap
      raise ValueError('wrapper loop when unwrapping {!r}'.format(f))
  E   ValueError: wrapper loop when unwrapping call
  </code></pre>
  
  <p>Call imported like this:</p>
  
  <pre class="lang-py prettyprint-override"><code>from unittest.mock import MagicMock, call
  </code></pre>
  
  <p>I looked at this question <a href="https://stackoverflow.com/questions/49271586/valueerror-wrapper-loop-when-unwrapping">ValueError: wrapper loop when unwrapping</a>. Rewriting <code>__getattr__</code> does not look like a clean solution for me.</p>
  
  <p>I import and use <code>call</code> differently, as a workaround, which helps:</p>
  
  <pre class="lang-py prettyprint-override"><code>from unittest import mock
  
  ...
  mock.call(1)
  ...
  </code></pre>
  
  <p>I wonder are there any better/cleaner options to solve the problem?</p>