Changed the Viewer::realize() calls across to not using the threading paramter

leaving it up to the Viewer to specify the mode (which by default is MultiThreaded).
Added a check for the presence of osgParticle systems so that threading is
disabled in this case.

include/osgParticle/VariableRateCounter

@@ -29,6 +29,7 @@ namespace osgParticle
         inline VariableRateCounter();
         inline VariableRateCounter(const VariableRateCounter &copy, const osg::CopyOp &copyop = osg::CopyOp::SHALLOW_COPY);
         
+        virtual const char *libraryName() const { return "osgParticle"; }
         virtual const char *className() const { return "VariableRateCounter"; }
         virtual bool isSameKindAs(const osg::Object *obj) const { return dynamic_cast<const VariableRateCounter *>(obj) != 0; }