Add executeConfirm method to perform multi-sig in 1 transaction

[bencxr]

Support for executing and confirmation an outgoing send from the wallet in a single transaction.
msg.sender is used for one of the signatures and data with ecrecover is used for another "signature".

How to generate the signature with eth.sign:
uint expireTime = 1863771845; // 10 years in the future
uint sequenceId = 1; // or the next sequence Id obtained using getNextSequenceId();
bytes32 sha3 = sha3(to, value, data, expireTime, sequenceId); // see tests for examples how to build this
bytes signature = eth.sign(owner1, sha3); // sign the sha3 using owner1

Example usage in tests:
https://github.com/BitGo/eth-multisig-v2/blob/master/test/wallet.js#L1075

[veox]

Sorry, too tired to continue line-by-line right now, but I see there's the same tendency (as in #65) to omit constant and internal specifiers; and using var in cycles (most places I saw comparing to c_maxSequenceIdWindowSize, which seems to be a uint constant of 10, which could slide).

[bencxr]

Thanks, I just addressed those concerns. However the bulk of this code does more heavy lifting so would appreciate a review of the new methods.

[chriseth]

I would prefer this change to be more modular. Would it be a possibility to create a "confirmation" module that handles the actual confirmations - which can be done using signatures only or direct calls?

[vbuterin]

Great work; this is something that is very much needed.

+1 to chriseth's comment that this could be more modular. Also, a nicer way of doing all of this might be to have the confirm function take an array of signatures, which could be empty (ie. the only confirm is the confirm from the tx sender), have 1 sig, or have multiple sigs; this way we need fewer functions.

[bencxr]

@vbuterin currently solidity does not support an array of bytes (signatures). It's actually rather easy to cal/use this method now, and I would rather not add additional complexity on the client if possible. We could add on a function taking when solidity does support array of bytes.