change VertexRef elements to unsigned values to fix compile warnings

SConstruct

@@ -1,6 +1,6 @@
 
 # vim:filetype=python
 
-env = Environment(LIBS = ['GL'])
+env = Environment(LIBS = ['GL'], CXXFLAGS = ['-Wall'])
 
 env.Program('driver', Glob('*.cc'))

WFObj.cc

@@ -122,7 +122,7 @@ WFObj::~WFObj()
 
 void WFObj::clear()
 {
-    for (int i = 0; i < sizeof(m_vertices)/sizeof(m_vertices[0]); i++)
+    for (size_t i = 0; i < sizeof(m_vertices)/sizeof(m_vertices[0]); i++)
         m_vertices[i].clear();
     m_faces.clear();
     m_materials.clear();

WFObj.h

@@ -92,9 +92,9 @@ protected:
     {
         public:
             VertexRef() : vertex(0), texture(0), normal(0) {}
-            int vertex;
-            int texture;
-            int normal;
+            size_t vertex;
+            size_t texture;
+            size_t normal;
             bool operator<(const VertexRef & other) const;
     };