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

serializer/cross/serializer_binary.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 87 matching lines @@
       return;
     }
 
     stream.WriteByte(field_id);
     stream.WriteByte(field.num_components());
   }
 
   // Write out the number of elements
   stream.WriteLittleEndianUInt32(num_elements);
 
-  // Make note of stream position at end of header
-  size_t data_start_position = stream.GetStreamPosition();
-
   // Write out the data for each field
   // Write out the specification for the fields
   for (size_t i = 0; i < num_fields; ++i) {
     const Field &field = *buffer.fields()[i];
 
     MemoryBuffer<uint8> field_data(field.size() * num_elements);
     uint8 *destination = field_data;
 
     // Figure out what type of field it is, and get the data
     // appropriately
@@ skipping 136 matching lines @@
 
     for (size_t j = 0; j < influence_count; ++j) {
       const Skin::Influence &influence = influences[j];
       stream.WriteLittleEndianInt32(influence.matrix_index);
       stream.WriteLittleEndianFloat32(influence.weight);
     }
   }
 }
 
 }  // namespace o3d