Attempts to fix compile problems under IRIX due to namespace problems.

src/osgSim/DOFTransform.cpp

@@ -13,6 +13,7 @@
 #include <osgSim/DOFTransform>
 
 using namespace osgSim;
+using namespace osg;
 
 DOFTransform::DOFTransform():
     _limitationFlags(0), 

src/osgSim/MultiSwitch.cpp

@@ -15,6 +15,7 @@
 #include <algorithm>
 
 using namespace osgSim;
+using namespace osg;
 
 MultiSwitch::MultiSwitch():
     _newChildDefaultValue(true),

src/osgSim/VisibilityGroup.cpp

@@ -17,6 +17,7 @@
 #include <osgUtil/IntersectVisitor>
 
 using namespace osgSim;
+using namespace osg;
 
 VisibilityGroup::VisibilityGroup():
     _volumeIntersectionMask(0xFFFFFFFF),