message: fixed bug with the way private key presence was checked in signTransaction
  Reviewers: benchan, barath
  Subscribers: ben
diff: @@ -317,8 +317,8 @@ Wallet.prototype.signTransaction = function(params, callback) {
  }
  var userPrv = params.prv;
  if (userPrv && typeof userPrv !== 'string') {
  - throw new Error('txPrebuild must be a string');
  - } else {
  + throw new Error('prv must be a string');
  + } else if (!userPrv) {
  if (!userKeychain || typeof userKeychain !== 'object') {
  throw new Error('keychain must be an object');
  }
  