Clear groups on reset for AccumulatingDocIdPusher and return named resources as unmodifiable  collection
code review : https://codereview.appspot.com/69890046/

These changes originated from code review for FS Adaptor.
diff --git a/test/com/google/enterprise/adaptor/sharepoint/AccumulatingDocIdPusher.java b/test/com/google/enterprise/adaptor/sharepoint/AccumulatingDocIdPusher.java
index 6e30985..9ffb8c3 100644
--- a/test/com/google/enterprise/adaptor/sharepoint/AccumulatingDocIdPusher.java
+++ b/test/com/google/enterprise/adaptor/sharepoint/AccumulatingDocIdPusher.java
@@ -68,7 +68,7 @@
   }
   
   public List<Map<DocId, Acl>> getNamedResources() {
-    return namedResouces;
+    return Collections.unmodifiableList(namedResouces);
   }
 
   public Map<GroupPrincipal, Collection<Principal>> getGroups() {
@@ -78,6 +78,7 @@
   public void reset() {
     records.clear();
     namedResouces.clear();
+    groups.clear();
   }
 
   @Override