b=391557. p=johnmarsh. r=mfinkle, dietrich. a=mconnor. change Annotation.get to return null instead of throwing exceptions (whitespace cleanup too)

browser/fuel/src/fuelApplication.js

@@ -801,7 +801,9 @@ Annotations.prototype = {
   },
 
   get : function(aName) {
-    return Utilities.annotations.getItemAnnotation(this._id, aName);
+    if (this.has(aName))
+      return Utilities.annotations.getItemAnnotation(this._id, aName);
+    return null;
   },
 
   set : function(aName, aValue, aExpiration) {

browser/fuel/test/browser_Bookmarks.js

@@ -85,6 +85,7 @@ function test() {
   testBookmark.annotations.remove("testing/bookmark");
   ok(!testBookmark.annotations.has("testing/bookmark"), "Checking existence of removed annotation");
   is(gLastBookmarkAction, "testing/bookmark", "Check event handler for removing annotation");
+  is(testBookmark.annotations.get("testing/bookmark"), null, "Check existence of a missing annotation");
 
   // quick annotation type tests
   testBookmark.annotations.set("testing/bookmark/string", "annotate-this", 0);