Small tweak to TextPane to allow insert at the end of a paragraph to add to
a TextNode that is positioned there, instead of always creating a new TextNode.
This allows a bit more efficiency when doing things like syntax coloring of
a document.

This is a merge of revision 1523284 from branches/2.0.x to trunk.



git-svn-id: https://svn.apache.org/repos/asf/pivot/trunk@1523288 13f79535-47bb-0310-9956-ffa450edef68