Revision 1839358

Several fixes to TextPane:
* Fix previous changes that made ImageNode (and ComponentNode) into subclasses
  of Block so that they could be inserted directly into a document.  This was
  shown to be a flawed strategy, and ComponentNode was fixed by a previous
  change.  Make ImageNode back into a direct subclass of Node.
* Add an implementation of "getCharacters" to ImageNode to satisfy the abstract
  declaration of Node (this is relatively new).
* Change Document to allow ImageNode (and previously ComponentNode) as possible
  direct inserts into a Document
* Add a method to ClassUtils to check any number of possible classes for an
  "instanceOf" check, and use this in Document.
* Unrelated, but discovered in the same test program:  fix CharUtils.selectWord
  to gracefully handle a null input sequence.