References and Links need IDs

[stu42j]

If the URN-style IDs are going to be useful, they need to be included in References and Links. Based on the schema, it seems the id attribute is optional but I've never actually seen one.

Here is an example of what I mean:

<Catalog
 xmlns="http://www.vmware.com/vcloud/v1.5"
 name="ExampleCatalog"
 type="application/vnd.vmwar...




 id="urn:vcloud:catalogitem:221"
 type="application/vnd.vmware.vcloud.catalogItem+xml"
 name="Ubuntu Template with vsftpd"
 href="https...