Add test cases around new EXTCODEHASH behavior

[fulldecent]

The behavior of this implementation was changed slightly with the switch to EXTCODEHASH. Let's document this using test cases.

Mocks:

• Contract R
  • Has a token receive function which emits an event Received
• Contract A is R
  • Has constructor
    1. Deploys NFToken
    2. Mints token id=1
    3. Transfers token id=1 to self
• Contract B
  • Has constructor
    1. Deploys NFToken
    2. Deploys R
    3. Transfers token id=1 to R

Tests:

1. Test 1
   1. Transaction 1 -- Deploy NFToken
   2. Transaction 2 -- Mint token id=1
   3. Transaction 3 -- Deploy Contract R
   4. Transaction 4 -- Transfer token id=1 to R
   5. Expect NO event on Constantinople
2. Test 2
   1. Transaction 1 -- Deploy NFToken
   2. Transaction 2 -- Mint token id=1
   3. Transaction 3 -- Deploy Contract R
   4. Expect NO event on Constantinople
3. Test 3
   1. Transaction 1 -- Deploy Contract B
   2. Expect event on Constantinople (but no event with same test using old version of implementation)

[xpepermint]

@fulldecent do you have time to add these? The rest of the team is overbooked at the moment.

[fulldecent]

You bet, I'm on it.

[frangio]

I think there should be another test for a transfer to a contract that has selfdestructed, since the result of extcodehash will be different.

[fulldecent]

Progress on a test is here #241

Requesting help with this line:

https://github.com/0xcert/ethereum-erc721/pull/241/files#diff-1eaa4a12fea6a0a32769fb056436a04aR408

I need to check logs from a deploy transaction.