AWS_S3_FILE_OVERWRITE should be False by default

[WhyNotHugo]

All Django's builtin storages do not overwrite files by default -- they append a number when there's collision.

I've been using S3Boto3Storage for quite some time, and suddenly found that many of my files were mixed up -- models seems to have a reference to the wrong on-disk file. After some research, it turns out this particular storage overwrites files by default.

This is very undesirable behaviour -- it's the opposite of the default used by Django, and can (and has) easily result in data loss.

Issues with the current default:

• It's the opposite of what Django does.
• It's a "delete user data by default", which is as bad as it sounds.
• It's too easy to screw up, since there's no clue that this storage behaves differently -- as I said, I only found out after researching some data loss.

[hardenchant]

Today, this default value led to incorrect behavior in my application. This is not normal. 😞