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

core/cross/bitmap_png.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 181 matching lines @@
     format = Texture::XRGB8;
     // Add alpha byte after each RGB triplet
     png_set_filler(png_ptr, 0xff, PNG_FILLER_AFTER);
   }
   png_set_bgr(png_ptr);
   dst_components = 4;
 
   // Turn on interlace handling.  REQURIED if you are not using
   // png_read_image().  To see how to handle interlacing passes,
   // see the png_read_row() method below:
-  int png_number_passes = png_set_interlace_handling(png_ptr);
+  png_set_interlace_handling(png_ptr);
 
   // Execute any setup steps for each Transform, i.e. to gamma correct and
   // add the background to the palette and update info structure.  REQUIRED
   // if you are expecting libpng to update the palette for you (ie you
   // selected such a transform above).
   png_read_update_info(png_ptr, info_ptr);
 
   // Allocate storage for the pixels.
   unsigned int num_mipmaps =
       generate_mipmaps ? GetMipMapCount(png_width, png_height) : 1;
@@ skipping 79 matching lines @@
 
   png_infop info_ptr = png_create_info_struct(png_ptr);
   if (!info_ptr) {
     DLOG(ERROR) << "Could not create PNG info structure.";
     png_destroy_write_struct(&png_ptr,  png_infopp_NULL);
     fclose(fp);
     return false;
   }
 
   scoped_array<png_bytep> row_pointers(new png_bytep[height_]);
-  for (unsigned int i = 0; i < height_; ++i) {
+  for (int i = 0; i < height_; ++i) {
     row_pointers[height_-1-i] = image_data_.get() + i * width_ * 4;
   }
 
   if (setjmp(png_jmpbuf(png_ptr))) {
     // If we get here, we had a problem reading the file.
     DLOG(ERROR) << "Error while writing file " << filename << ".";
     png_destroy_write_struct(&png_ptr, &info_ptr);
     fclose(fp);
     return false;
   }
 
   png_init_io(png_ptr, fp);
 
   png_set_IHDR(png_ptr, info_ptr, width_, height_, 8,
                PNG_COLOR_TYPE_RGB_ALPHA, PNG_INTERLACE_NONE,
                PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
   png_set_bgr(png_ptr);
   png_set_rows(png_ptr, info_ptr, row_pointers.get());
   png_write_png(png_ptr, info_ptr, PNG_TRANSFORM_IDENTITY, png_voidp_NULL);
 
   png_destroy_write_struct(&png_ptr, &info_ptr);
   fclose(fp);
   return true;
 }
 
 }  // namespace o3d