Initial version of transactions. Shell command implemented as an example. Still needs channel cleanup on app side, handling a device dying in the middle of a transaction, and getting device list back to normal.

lib/wire/util.js

@@ -29,6 +29,14 @@ var wireutil = {
 , envelope: function(message) {
     return new wire.Envelope(message.$code, message.encode()).encodeNB()
   }
+, transaction: function(channel, message) {
+    return new wire.Envelope(
+        message.$code
+      , message.encode()
+      , channel
+      )
+      .encodeNB()
+  }
 , makeDeviceLogMessage: function(serial, entry) {
     return wireutil.envelope(new wire.DeviceLogMessage(
       serial