Revision 604678

Streamlining/Correction of the changes made in r603926
- delegate validation of the fo:wrapper's children to the parent: added static FONode.validateChildNode()
- narrow the condition for processing text-childnodes: 
  this is not only constrained to fo:flow and fo:static-content, but the same goes 
  for a fo:wrapper that is a direct descendant of a fo:block-container or fo:inline-container, 
  which only allow block-level content (interpretation)
- minor javadoc fixups/improvements