Protect against broken prefix table.

git-svn-id: https://svn.apache.org/repos/asf/jena/trunk@1612831 13f79535-47bb-0310-9956-ffa450edef68
Add <link> configuration to Javadoc plugin so individually generated javadocs are cross linked to each other (JENA-683)

git-svn-id: https://svn.apache.org/repos/asf/jena/trunk@1612836 13f79535-47bb-0310-9956-ffa450edef68