Verify the claim process and trust level for our inclusion proofs

[InoMurko]

• Push/pull funds from contact after submitting claims, is an additional step necessary
• can reorgs enable someone to take advantage of no waiting period?
• safe blocknum upperbound, automate with a margin?

[kevsul]

An Automatic Safe Block number appears to be acceptable in the case of a certain amount of trust between the Quasar Owner and Plasma Operator

See #734

[kevsul]

• Push/pull funds from contact after submitting claims, is an additional step necessary?

Assuming that there's no waiting period, I don't think there's any benefit in adding the extra step to require the user to pull their funds. Reentrancy attack was raised as a concern, but that can be avoided by being careful and using SafeEthTransfer.

[kevsul]

• can reorgs enable someone to take advantage of no waiting period?

The waiting period protects against a double spend of the exiting utxo.

Given that our trust model for this Quasar is based on the Quasar owner trusting the Plasma operator, the waiting period is unnecessary because an honest Plasma operator won't allow a double spend to happen.

An honest Plasma operator will also not attempt to rollback or withhold blocks, so as long as the exiting user can present an inclusion proof of the tx sent to the Quasar owner, reorgs on the main chain should not provide an opportunity for attack.