Validation Bugs

[chadlagore]

Validation May Not be Perfect 🤔

Put known bugs here!

• For transaction validation rule regarding re-spend attacks, hashing the transactions isn't sufficient protection against a re-spend. We also need to know if the inputs have been spent elsewhere (simply hashing won't catch this). More info 👇 https://github.com/ubclaunchpad/cumulus/blob/dev/blockchain/validation.go#L148

[bfbachmann]

I think @david-julien has already handled this in his PR
https://github.com/ubclaunchpad/cumulus/pull/112/files#diff-3a5c8ea459d421751fb70343be214598R39