resources: Overhaul legacy code around the resource API

This patch makes a number of changes in the engine surrounding the
resource API. In particular:

* Cleanup of send/read event.
* Cleanup of DoSend (now Event) in the Watch method.
* Events are now more consistently pointers.
* Exiting within Watch is now done in a single place.
* Multiple incoming events will be combined into a single action.
* Events in flight during an action are played back after CheckApply.
* Addition of Close method to API

This gets things ready for rate limiting and semaphore metaparams!

resources/hostname.go

@@ -111,7 +111,7 @@ func (obj *HostnameRes) Init() error {
 }
 
 // Watch is the primary listener for this resource and it outputs events.
-func (obj *HostnameRes) Watch(processChan chan event.Event) error {
+func (obj *HostnameRes) Watch(processChan chan *event.Event) error {
 	cuid := obj.ConvergerUID() // get the converger uid used to report status
 
 	// if we share the bus with others, we will get each others messages!!
@@ -148,8 +148,8 @@ func (obj *HostnameRes) Watch(processChan chan event.Event) error {
 		case event := <-obj.Events():
 			cuid.SetConverged(false)
 			// we avoid sending events on unpause
-			if exit, _ := obj.ReadEvent(&event); exit {
-				return nil // exit
+			if exit, _ := obj.ReadEvent(event); exit != nil {
+				return *exit // exit
 			}
 			send = true
 			obj.StateOK(false) // dirty
@@ -162,10 +162,7 @@ func (obj *HostnameRes) Watch(processChan chan event.Event) error {
 		// do all our event sending all together to avoid duplicate msgs
 		if send {
 			send = false
-
-			if exit, err := obj.DoSend(processChan, ""); exit || err != nil {
-				return err // we exit or bubble up a NACK...
-			}
+			obj.Event(processChan)
 		}
 	}
 }