to protect against accessing while writing which was segfaulting in VPB
specifically in void ThreadPool::run(osg::Operation* op)
in the waiting loop
while (_operationQueue->getNumOperationsInQueue() >= _maxNumberOfOperationsInQueue)
"
to the view to be done during syncronous updateTraversal().
This feature can be used for doing things like merging subgraphs that have been loaded
in a background thread.
Created a new GraphicsThread subclass from OperationThread which allows the
GraphicsContext specific calls to be moved out of the base OperationThread class.
Updated the rest of the OSG to respect these changes.
