Merge pull request #334 from mathieu/ValidateProgramTooEarly

Under macOS the glValidateProgram reports too many errors

src/osg/Program.cpp

@@ -517,9 +517,10 @@ void Program::apply( osg::State& state ) const
         // for shader debugging: to minimize performance impact,
         // optionally validate based on notify level.
         // TODO: enable this using notify level, or perhaps its own getenv()?
+#ifndef __APPLE__
         if( osg::isNotifyEnabled(osg::INFO) )
             pcp->validateProgram();
-
+#endif
         pcp->useProgram();
         state.setLastAppliedProgramObject(pcp);
     }