XWIKI-10822: xdocAuthors id is duplicate

These IDs are used across skins, so the names should be preserved across skins. You cannot just add a new one. 
Also we don't encourage the use of ID's. We are preserving the same behavior only for compatibility reasons. 

This bugs has already been fixed in http://jira.xwiki.org/browse/XWIKI-10815
Closing the Pull Request. 

You should download the latest snapshot to test the recent modifications, see http://maven.xwiki.org/snapshots/org/xwiki/enterprise/xwiki-enterprise-jetty-hsqldb/6.2-SNAPSHOT/

Thanks.