Introduced OSG_WARN, OSG_NOTICE, OSG_INFO, OSG_DEBUG convinience macros that map to OSG_NOTIFY(osg::WARN) etc.
Introduced the OSG_NOTIFY_DISABLE Cmake variable + include/osg/Config #define to control whether the OpenSceneGraph build
should disable the notification system completely. By setting OSG_NOTIFY_DISABLE to ON in CMake and then rebuilding the
the OSG you can get a slightly smaller (~1%) and more slightly efficient library which can be good for shipping applications,
but with downside of reduced ability to detect runtime problems and their causes.