Ensure ForkedBlockchain.prototype.getAccount works

[mikeseese]

This issue pulls out #3 from #483 (comment):

Yes, I meant ForkedBlockchain.prototype.getAccount. There might be a separate bug in this fn, I haven't checked if there are tests for this scenario yet:

• contract account A exists at block 9 on the original chain. it has a non-zero balance
• we fork at block 10
• we selfdestruct() the contract on our fork at block 11, thus transferring its value to another address.
• getAccount(account A, block 12) may return the account from the original chain. A call to eth_getBalance may return the non-zero account value.

[mikeseese]

This was released in https://github.com/trufflesuite/ganache-core/releases/tag/v2.12.2-beta.0