Added helper to get transactionally-bound List, Map and Set resources

- Generics allow the following, for instance:
   Map<NodeRef,List<QName>> filters = TransactionalResourceHelper.getMap(KEY_NODEREF_FILTER);


git-svn-id: https://svn.alfresco.com/repos/alfresco-enterprise/alfresco/HEAD/root@13794 c4b6b30b-aa2e-2d43-bbcb-ca4b014f7261

source/java/org/alfresco/repo/transaction/AlfrescoTransactionSupport.java

@@ -202,8 +202,11 @@ public abstract class AlfrescoTransactionSupport
      *  
      * @param key the thread resource map key
      * @return Returns a thread resource of null if not present
+     * 
+     * @see TransactionalResourceHelper         for helper methods to create and bind common collection types
      */
-    public static Object getResource(Object key)
+    @SuppressWarnings("unchecked")
+    public static <R extends Object> R getResource(Object key)
     {
         // get the synchronization
         TransactionSynchronizationImpl txnSynch = getSynchronization();
@@ -216,7 +219,7 @@ public abstract class AlfrescoTransactionSupport
                     "   key: " + key + "\n" +
                     "   resource: " + resource);
         }
-        return resource;
+        return (R) resource;
     }
     
     /**