finished: _update_kv_node. need testing
finished: _update_kv_node. need testing

ethermarket/pyethereum,ebuchman/daoist_protocol,harlantwood/pyethereum,karlfloersch/pyethereum,shahankhatch/pyethereum,inzem77/pyethereum,ethers/pyethereum,ddworken/pyethereum,vaporry/pyethereum,shahankhatch/pyethereum,pipermerriam/pyethereum,karlfloersch/pyethereum,ckeenan/pyethereum,ebuchman/daoist_protocol,ethereum/pyethereum,holiman/pyethereum,jnnk/pyethereum,pipermerriam/pyethereum,ethereum/pyethereum