title: Python PIL - Save to mimetype "image/jpeg", not "image/pjpeg"
body: <p>I'm currently working with Tweepy in trying to update a profile picture. Tweepy supports up to three different mimetype formats, '<strong>image/gif</strong>', '<strong>image/jpeg</strong>', '<strong>image/png</strong>'. </p>
  
  <p>Using PIL, I'm trying to convert the image to <strong>'image/jpeg'</strong>, though everytime I attempt to use PIL to conver the image it comes out as <strong>'image/pjpeg'</strong> instead. I've tried adding pjpeg to the allowed list on Tweepy but it doesn't understand how to handle it.</p>
  
  <p>How can I convert an image with PIL to <strong>'image/jpeg'</strong>, and not <strong>'image/pjpeg'</strong> mimetype?</p>
  
  <pre><code>from PIL import Image
  import mimetypes
  
  pic = Image.open(rootDir + "pic.png")
  pic = pic.convert("RGB")
  pic.save(rootDir + "new.jpg", 'jpeg', progressive=False)
  
  print mimetypes.guess_type(rootDir + "new.jpg")
  </code></pre>