captcha.views.captcha_image should be decorated with never_cache

[GoogleCodeExporter]

The view captcha.views.captcha_image and captcha.views.captcha_audio should be 
decorated with django.views.decorators.cache.never_cache, to avoid the image 
being cached by browsers and proxies, mostly when using global cache settings.

Original issue reported on code.google.com by gmandx on 14 Jun 2011 at 5:22

[GoogleCodeExporter]

Why would browsers cache the image and the audio rendering, as the hashes of 
the captcha are in their URL, granting an unique and distinct URL?

Original comment by mbonetti on 15 Jun 2011 at 7:11