Merge branch 'fix-clang-warning-gnuext' into 'master'

Fix clang warning by avoiding GNU extension.

See merge request !56

libs_required/ACG/GL/globjects.hh

@@ -151,7 +151,7 @@ public:
 
   char* offset(unsigned int _offset) const
   {
-    return ((char*)NULL + _offset);
+    return reinterpret_cast<char*>(_offset);
   }
 
   GLuint id() const {return vbo;}