Bridge plugin: announce changes received for existing annotations

When we receive updated versions of existing annotations from the
other side of the bridge, not only merge those changes,
but announce them with the appropriate event, too.

Based on changes originally introduced here:
https://github.com/hypothesis/h/commit/1d4e9f32cc4f8c7db5ffdac7adad90e9cbf88db6#diff-5

h/js/plugin/bridge.coffee

@@ -156,11 +156,18 @@ class Annotator.Plugin.Bridge extends Annotator.Plugin
     ## Notifications
     .bind('loadAnnotations', (txn, annotations) =>
       # First, parse the existing ones, for any updates
-      this._parse a for a in annotations when @cache[a.tag]
+      oldOnes = (this._parse a for a in annotations when @cache[a.tag])
+
+      # Announce the changes in old annotations
+      if oldOnes.length
+        @selfPublish = true
+        @annotator.publish 'annotationsLoaded', [oldOnes]
+        delete @selfPublish
+
       # Then collect the new ones
-      annotations = (this._parse a for a in annotations when not @cache[a.tag])
-      if annotations.length
-        @annotator.loadAnnotations annotations
+      newOnes = (this._parse a for a in annotations when not @cache[a.tag])
+      if newOnes.length
+        @annotator.loadAnnotations newOnes
     )
 
     .bind('showEditor', (ctx, annotation) =>
@@ -285,6 +292,11 @@ class Annotator.Plugin.Bridge extends Annotator.Plugin
     this
 
   annotationsLoaded: (annotations) =>
+    return if @selfPublish
+    unless annotations.length
+      console.log "Useless call to 'annotationsLoaded()' with an empty list"
+      console.trace()
+      return
     this._notify
       method: 'loadAnnotations'
       params: (this._format a for a in annotations)