This fixes a number of things that are warnings in the Mac compiler....

core/cross/shape.cc

 /*
  * Copyright 2009, Google Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 60 matching lines @@
   ElementArray elements;
   elements.reserve(elements_.size());
   std::copy(elements_.begin(),
             elements_.end(),
             std::back_inserter(elements));
   return elements;
 }
 
 void Shape::SetElements(const ElementArray& elements) {
   elements_.resize(elements.size());
-  for (int i = 0; i != elements.size(); ++i) {
+  for (unsigned int i = 0; i != elements.size(); ++i) {
     elements_[i] = Element::Ref(elements[i]);
   }
 }
 
 namespace {
 class FindByMaterial {
  public:
   explicit FindByMaterial(Material* material) : material_(material) { }
 
   bool operator() (const DrawElement* draw_element) {
@@ skipping 11 matching lines @@
     const DrawElementRefArray& draw_elements = element->GetDrawElementRefs();
     if (std::find_if(draw_elements.begin(),
                      draw_elements.end(),
                      FindByMaterial(material)) == draw_elements.end()) {
       elements_[pp]->CreateDrawElement(pack, material);
     }
   }
 }
 
 }  // namespace o3d