Fixed the osg::Light so that it requires the user to explicitly define which

OpenGL light is being operated on, and also now relies upong the standard
osg::State handling of OpenGL modes to switch on the appropriate lights.

The previous static counter mechansim for the light number was causing a
redundent light to be created when the osg plugin created the first osg::Light
to use a prototype for other osg::Light's to be cloned from in the
.osg plugin execution.

The static count mechanism also prevent the lights modes being controlled
independantly from the setting of the light paramters themselves.  This
meant that a light once created was global, and couldn't be turned off
locally via the OSG's support for OpenGL mode enabling/disabling.  This
has been overcome with the new implementation, the user has complete
flexiblity of when and where to use the different lights at their
disposal.

src/osgPlugins/osg/Light.cpp

@@ -32,6 +32,16 @@ bool Light_readLocalData(Object& obj, Input& fr)
 
     Light& light = static_cast<Light&>(obj);
 
+    if (fr[0].matchWord("light_num"))
+    {
+        int lightnum=0;
+        if (fr[1].getInt(lightnum))
+        {
+            light.setLightNum(lightnum);
+            fr += 2;
+            iteratorAdvanced = true;
+        }
+    }
 
 #define ReadVec4(A,B) {  \
     if (fr[0].matchWord(B) && \
@@ -96,6 +106,8 @@ bool Light_writeLocalData(const Object& obj,Output& fw)
 {
     const Light& light = static_cast<const Light&>(obj);
 
+    fw.indent() << "light_num " << light.getLightNum() << std::endl;
+
     // Vec4's
     fw.indent() << "ambient " << light.getAmbient() << std::endl;
     fw.indent() << "diffuse " << light.getDiffuse() << std::endl;