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

core/cross/gl/sampler_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 78 matching lines @@
       // fall through
     case Sampler::ANISOTROPIC:  // Anisotropy is handled in SetTextureAndStates
     case Sampler::LINEAR:
       if (mip_filter == Sampler::NONE)
         return GL_LINEAR;
       else if (mip_filter == Sampler::POINT)
         return GL_LINEAR_MIPMAP_NEAREST;
       else if (mip_filter == Sampler::LINEAR)
         return GL_LINEAR_MIPMAP_LINEAR;
   }
+  DCHECK(false);
+  return GL_NONE;
 }
 
 unsigned int GLMagFilter(Sampler::FilterType o3d_filter) {
   switch (o3d_filter) {
     case Sampler::POINT:
       return GL_NEAREST;
     case Sampler::LINEAR:
       return GL_LINEAR;
     default:
       DLOG(ERROR) << "Unknown filter " << static_cast<int>(o3d_filter);
@@ skipping 83 matching lines @@
     //     time.
     GLenum target = GLTextureTarget(the_texture);
     if (target) {
       GLenum texture_unit = cgGLGetTextureEnum(cg_param);
       glActiveTextureARB(texture_unit);
       glBindTexture(target, 0);
     }
   }
 }
 }  // namespace o3d