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

core/cross/gl/utils_gl.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 176 matching lines @@
 
 // Given a vertex attribute stream, convert it to a Stream::Semantic number
 // and index. This is an imprecise operation.
 Stream::Semantic GLVertexAttributeToStream(const unsigned int attr,
                                            int *index) {
   // kMaxAttrIndex is available from:
   //    glGetIntegerv(GL_MAX_VERTEX_ATTRIBS, &max_vertex_attribs);
   //
   // TODO: make this a runtime provided value discovered during
   // Renderer creation.
-  const int kMaxAttrIndex = 15;
+  const unsigned int kMaxAttrIndex = 15u;
   if (attr > kMaxAttrIndex) {
     //TODO: Figure out how to get errors out of here to the client.
     DLOG(ERROR) << "Invalid vertex attribute index.";
     *index = 0;
     return Stream::UNKNOWN_SEMANTIC;
   }
   *index = attr_map_vp_40[attr].index;
   return attr_map_vp_40[attr].semantic;
 }
 
@@ skipping 11 matching lines @@
     DLOG(ERROR) << logmessage << ": " << error_string;
     if (error == CG_COMPILER_ERROR) {
       DLOG(ERROR) << "Compiler message:\n" << cgGetLastListing(cg_context);
     }
   }
 }
 
 #endif
 
 }  // namespace o3d