Hash issues

[biglyderv]

• Two or more assets with the same content or hash are sent via POST to assets.scratch.mit.edu multiple times, when it would be optimal to send the asset one time.
• It is possible to engineer a MD5 collision, resulting in two different assets having the same asset URL; this can cause issues when one overrides the other.

[Brohann3214]

I've experimented with this myself and found that when I upload an asset with the same hash as another, the original asset receives a new MD5 hash. The files remain identical, so I assume the original is salted and re-hashed. Therefore, we don't have to worry about an MD5 collision.