X-Selection (also known as mouse selection or PRIMARY) has made its way into subversion. The regular clipboard and x-selection work concurrently, you can enable or disable any at will. The history menu will mark the item currently in x-selection in italics if it is not the same as your clipboard contents.
In addition, Parcellite now checks the history to check if a newly copied item is already in history. I will later make it so if it is already in history it will get bumped up as the newest item and its older copies be deleted.