Check coin data is compatible with commitment

[riemann89]

In testEtherMixing.py and testERCTokenMixing.py: when Charlie receives 1 ETH/1 ETHToken from BOB, he should

• Recompute the commitment from the coin's data (to check the validity of the payment)

• Make sure this recomputed commitment is equal to the commitment at address cm_address1BtB

[rrtoledo]

We have to be very careful here because this can easily lead to deanonymising a coin. This could be discussed in #144 .

My first ideas to avoid deanonymisation so would be to either:

• pull the last commitments after a sufficiently large random delay (after receiving a coin) and check that our recomputed commitment is in the retrieved list
• pull the last commitments at regular intervals (independent of receiving a coin)
• have the Mix contract emit the new root and commitment

[dtebbs]

Should be addressed in fb90b95 (part of #130).
(Also discussed in #144)

[AntoineRondelet]

@rrtoledo as mentioned by @dtebbs this has already been discussed here: #130 (comment)

[AntoineRondelet]

Closing this issue since it has been addressed in #130