Hardened SHA-1

[Sainan]

Git now uses this variant of SHA-1 that produces a different hash if a 'disturbance' is detected: https://github.com/cr-marcstevens/sha1collisiondetection/blob/master/lib/sha1.c#L1729-L1764

A practical example of 2 messages that produce the same hash with normal SHA-1:

• https://sha-mbles.github.io/messageA
• https://sha-mbles.github.io/messageB