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

core/cross/gl/texture_gl.h

 /*
  * 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 101 matching lines @@
               const Bitmap &bitmap,
               bool resize_npot,
               bool enable_render_surfaces);
 
   // Updates a mip level, sending it from the backing bitmap to GL, rescaling
   // it if resize_to_pot_ is set.
   void UpdateBackedMipLevel(unsigned int level);
 
   // Returns true if the backing bitmap has the data for the level.
   bool HasLevel(unsigned int level) const {
-    DCHECK_LT(level, levels());
+    DCHECK_LT(static_cast<int>(level), levels());
     return (has_levels_ & (1 << level)) != 0;
   }
 
   RendererGL* renderer_;
 
   // The handle of the OpenGL texture object.
   GLuint gl_texture_;
 
   // A bitmap used to back the NPOT textures on POT-only hardware, and to back
   // the pixel buffer for Lock().
@@ skipping 56 matching lines @@
                 const Bitmap &bitmap,
                 bool resize_to_pot,
                 bool enable_render_surfaces);
 
   // Updates a mip level, sending it from the backing bitmap to GL, rescaling
   // it if resize_to_pot_ is set.
   void UpdateBackedMipLevel(unsigned int level, CubeFace face);
 
   // Returns true if the backing bitmap has the data for the level.
   bool HasLevel(unsigned int level, CubeFace face) const {
-    DCHECK_LT(level, levels());
+    DCHECK_LT(static_cast<int>(level), levels());
     return (has_levels_[face] & (1 << level)) != 0;
   }
 
   RendererGL* renderer_;
 
   // The handle of the OpenGL texture object.
   GLuint gl_texture_;
 
   // A bitmap used to back the NPOT textures on POT-only hardware, and to back
   // the pixel buffer for Lock().
   Bitmap::Ref backing_bitmap_;
 
   // Bitfields that indicates mip levels that are currently stored in the
   // backing bitmap, one per face.
   unsigned int has_levels_[6];
 };
 
 }  // namespace o3d
 
 #endif  // O3D_CORE_CROSS_GL_TEXTURE_GL_H__