Fix warning -Wunused-but-set-variable

include/osg/Plane:244:17: warning: variable 'noOn' set but not used [-Wunused-but-set-variable]
            int noOn = 0;
                ^
include/osg/Plane:273:17: warning: variable 'noOn' set but not used [-Wunused-but-set-variable]
            int noOn = 0;
                ^

Author: elsid

include/osg/Plane

@@ -241,15 +241,13 @@ class OSG_EXPORT Plane
 
             int noAbove = 0;
             int noBelow = 0;
-            int noOn = 0;
             for(std::vector<Vec3f>::const_iterator itr=vertices.begin();
                 itr != vertices.end();
                 ++itr)
             {
                 float d = distance(*itr);
                 if (d>0.0f) ++noAbove;
                 else if (d<0.0f) ++noBelow;
-                else ++noOn;
             }
 
             if (noAbove>0)
@@ -270,15 +268,13 @@ class OSG_EXPORT Plane
 
             int noAbove = 0;
             int noBelow = 0;
-            int noOn = 0;
             for(std::vector<Vec3d>::const_iterator itr=vertices.begin();
                 itr != vertices.end();
                 ++itr)
             {
                 double d = distance(*itr);
                 if (d>0.0) ++noAbove;
                 else if (d<0.0) ++noBelow;
-                else ++noOn;
             }
 
             if (noAbove>0)