title: ImportError: No module named '_version' when importing mechanize
body: <p>I installed mechanize via pip and get an errer when I import the module:</p>
  
  <pre><code>$ python
  Python 3.5.2 (default, Jun 28 2016, 08:46:01) 
  [GCC 6.1.1 20160602] on linux
  Type "help", "copyright", "credits" or "license" for more information.
  &gt;&gt;&gt; import mechanize
  Traceback (most recent call last):
    File "&lt;stdin&gt;", line 1, in &lt;module&gt;
    File "/usr/lib/python3.5/site-packages/mechanize/__init__.py", line 119, in &lt;module&gt;
      from _version import __version__
  ImportError: No module named '_version'
  </code></pre>
  
  <p>The file <code>-version.py</code> is present in the site-packages directory:</p>
  
  <pre><code>$ ls /usr/lib/python3.5/site-packages/mechanize
  _auth.py               __init__.py           _response.py
  _beautifulsoup.py      _lwpcookiejar.py      _rfc3986.py
  _clientcookie.py       _markupbase.py        _sgmllib_copy.py
  _debug.py              _mechanize.py         _sockettimeout.py
  _firefox3cookiejar.py  _mozillacookiejar.py  _testcase.py
  _form.py               _msiecookiejar.py     _urllib2_fork.py
  _gzip.py               _opener.py            _urllib2.py
  _headersutil.py        _pullparser.py        _useragent.py
  _html.py               __pycache__           _util.py
  _http.py               _request.py           _version.py
  </code></pre>
  
  <p>What am I missing?</p>