#329 Support Link Entity

[Adam Tauno Williams]

Support the Link entity as an object type.
select object_link from doc where is_object_link =1;
...
3943250
433470
http://www.mozilla.org/projects/calendar/lightning/
http://www.mozilla.com/thunderbird/
http://weblogs.mozillazine.org/calendar/
1243750
5023060
5023030
...