Merged from OSG-2.8 branch changes to the use of ReadWriteMutex to Mutex in osgParticle::ParticleSystem.

svn command:

   svn merge -r 9725:9726 http://www.openscenegraph.org/svn/osg/OpenSceneGraph/branches/OpenSceneGraph-2.8

src/osgParticle/ConnectedParticleSystem.cpp

@@ -116,7 +116,7 @@ void ConnectedParticleSystem::drawImplementation(osg::RenderInfo& renderInfo) co
 {
     osg::State& state = *renderInfo.getState();
 
-    OpenThreads::ScopedReadLock lock(_readWriteMutex);
+    ScopedReadLock lock(_readWriteMutex);
 
     const Particle* particle = (_startParticle != Particle::INVALID_INDEX) ? &_particles[_startParticle] : 0;
     if (!particle) return;