Use timestamp when uploading duplicate filenames

[Areski Belaid]

When Uploading duplicate filenames, we use incremental method to determine the new filename, this method can slowly worsens over time if there is many files of the same name (ref https://code.djangoproject.com/ticket/23157) and it also give anyone informations about the files already uploaded.

This patch provide an easy way to obfuscated the names of the already uploaded files, which I think, may be the desired behavior we may want by default at some stage.
The global setting FILE_UPLOAD_USETIME_DUPLICATE try to remedy to this.

[Areski Belaid]

PR: ​https://github.com/django/django/pull/3018

This is a PoC, I will fix the tests if this is accepted.

[Tim Graham]

I think adding a hash rather than a timestamp (or even an option to replace the filename with a hash) would be a better solution. Users may not want to leak the time a file was uploaded. Adding a new setting is usually a no go if there is a way to avoid it, but perhaps the setting could be transitional as you've noted. It would be good to discuss this ticket on the DevelopersMailingList.

[Areski Belaid]

Thanks for the feedback, a suggested I opened a discussion here ​https://groups.google.com/forum/#!topic/django-developers/rjZbo4_W9jU

[Tim Graham]

We will address this in the fix for #23157. I am working on a patch.