title: Obnoxious CryptographyDeprecationWarning because of missing hmac.compare_time function everywhere
body: <p>Things were running along fine until one of my projects started printing this everywhere, at the top of every execution, at least once:</p>
  
  <pre><code>local/lib/python2.7/site-packages/cryptography/hazmat/primitives/constant_time.py:26: CryptographyDeprecationWarning: Support for your Python version is deprecated. The next version of cryptography will remove support. Please upgrade to a 2.7.x release that supports hmac.compare_digest as soon as possible.
  </code></pre>
  
  <p>I have no idea why it started and it's disrupting the applications'/tools' output, especially when it's being captured and consumed by other tools. Like many difficulties throughout time, I'm fairly certain it is related to <code>urllib</code> and, by association, <code>requests</code>. Worse, I have so many projects and cross-dependencies that I can't possibly update all of the imports and branches with the call to <code>warnings.filterwarnings()</code> to suppress the warning.</p>
  
  <p>I have Python 2.7.6 . Apparently this goes away in 2.7.7 . Only, I have some systems that have 2.7.6 where I <em>do not</em> see the warnings. So, something may or may not be disabling them in one version and I might've inadvertently replaced it with another version.</p>
  
  <p>My Ubuntu, Python, urllib, requests (with the security option), cryptography, and hmac are all identical versions/builds on systems that do print the warning and systems that do not.</p>
  
  <p>There appears to be no relevant warnings or announcements online and it seems like any related project is static/stable by this point (even though 'hmac' can be installed via PIP, it hasn't changed in eight years).</p>