title: Error installing scrapy 0.22 (on Ubuntu 12.04): 'gcc' failed with exit status 1
body: <p>When trying to install Scrapy from the command line using pip
  <br>
  <code>sudo pip install scrapy</code><br>
  I get the following error:
  <br>
  <code>error: command 'gcc' failed with exit status 1</code></p>
  
  <p>Looking a few lines up in the error output, I see that the error occurs while trying to install the 'cryptography' package which seems to be a dependency of pyOpenSSL</p>
  
  <p>I tried installing pyOpenSSL on its own and it gives the same error.
  Reading through the error output, I find that the likely cause of this error is a missing file:</p>
  
  <p><code>ffi.h: No such file or directory</code></p>
  
  <p>How should I proceed from here?</p>