title: Checking file type with django form: 'application/octet-stream' issue
body: <p>I'm using django validators and python-magic to check the mime type of uploaded documents and accept only pdf, zip and rar files.</p>
  
  <p>Accepted mime-types are:
  'application/pdf’, 
  'application/zip’, 'multipart/x-zip’, 'application/x-zip-compressed’, 'application/x-compressed',
   'application/rar’, 'application/x-rar’ 'application/x-rar-compressed’, 'compressed/rar',</p>
  
  <p>The problem is that sometimes pdf files seem to have 'application/octet-stream' as mime-type.
  'application/octet-stream' means generic binary file, so I can't simply add that mime type to the list of accepted files, because in that case also other files such es excel files would be accepted, and I don't want that to happen.</p>
  
  <p>How can I do in this case?</p>
  
  <p>Thanks in advance.</p>