Added a Visual Studio 2013 build error fix from the official repository

Implemented the fix from revision 512 of the official SVN repository on google code that allows Visual Studio 2013 to build protobuf without issues. 

Source:
https://code.google.com/p/protobuf/source/browse/trunk/src/google/protobuf/io/zero_copy_stream_impl_lite.cc?spec=svn512&r=512