Revision 219312

1) Handling of broken links is now forwarded to the bridge UserAgent Interface.
   This will cause problems if you don't derive off the UserAgentAdapter.
2) The default UserAgentAdapter now throws a BridgeException.  As a
   result the Transcoders now throw an error when an image can't be
   read rather than substituting the broken link document.
3) The JSVGCanvas now provides the BrokenLinkDocument - which should
   make it easier for people to customize the behaviour.
4) The JSVGCanvas now has an improved tooltip handling mechanism
   (although it still doesn't quite work as desired for the image element).