list of text drawables as a paragraph block, handles breaking of text into
individual lines automatically.
Changed the osg::Node::setUserData so that the data type has to be an
osg::Referenced, and removes the dependancy on osg::MemoryAdapter. I have
done this since it simplifies the OSG side of the interface and makes it
less like that the user might abuse the memory managment of the data. It
does however mean that user data will have by subclassed from Referenced,
and therefor may require users to have their own adapter to do this.
However, this little nuasance is worth the extra cleaness and robustness
afforded by going the osg::Referenced route.
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