Intoduced a new setGLExtensions template method to do a copy of void* pointer to

local function pointer to avoid compiler warnings related to case void*.

Moved various OSG classes across to using setGLExtensions instead of getGLExtensions,
and changed them to use typedef declarations in the headers rather than casts in
the .cpp.

Updated wrappers

include/osg/GLExtensions

@@ -68,6 +68,40 @@ inline void* getGLExtensionFuncPtr(const char *funcName,const char *fallbackFunc
     return getGLExtensionFuncPtr(fallbackFuncName);
 }
 
+
+template<typename T>
+bool setGLExtensionFuncPtr(T& t, const char* str1)
+{
+    void* data = osg::getGLExtensionFuncPtr(str1);
+    if (data)
+    {
+        memcpy(&t, &data, sizeof(T));
+        return false;        
+    }
+    else
+    {
+        t = 0;
+        return false;        
+    }
+}
+
+template<typename T>
+bool setGLExtensionFuncPtr(T& t, const char* str1, const char* str2)
+{
+    void* data = osg::getGLExtensionFuncPtr(str1,str2);
+    if (data)
+    {
+        memcpy(&t, &data, sizeof(T));
+        return false;        
+    }
+    else
+    {
+        t = 0;
+        return false;        
+    }
+}
+
+
 /** Return true if OpenGL "extension" is supported.
   * Note: Must only be called within a valid OpenGL context,
   * undefined behavior may occur otherwise.