Addd libraryName() method to osg::Object in preperation for the osgDB support

for node kits plugins.

include/osgParticle/Counter

@@ -17,6 +17,7 @@ namespace osgParticle
         inline Counter();
         inline Counter(const Counter &copy, const osg::CopyOp &copyop = osg::CopyOp::SHALLOW_COPY);
 
+        virtual const char *libraryName() const { return "osgParticle"; }
         virtual const char *className() const { return "Counter"; }
         virtual bool isSameKindAs(const osg::Object *obj) const { return dynamic_cast<const Counter *>(obj) != 0; }