Update //third_party/protobuf to version 3.

third_party/protobuf/vsprojects/convert2008to2005.sh

-#! /bin/sh -e
-
-# This script downgrades MSVC 2008 projects to MSVC 2005 projects, allowing
-# people with MSVC 2005 to open them.  Otherwise, MSVC 2005 simply refuses to
-# open projects created with 2008.  We run this as part of our release process.
-# If you obtained the code direct from version control and you want to use
-# MSVC 2005, you may have to run this manually.  (Hint:  Use Cygwin or MSYS.)
-
-for file in *.sln; do
-  echo "downgrading $file..."
-  sed -i -re 's/Format Version 10.00/Format Version 9.00/g;
-              s/Visual Studio 2008/Visual Studio 2005/g;' $file
-done
-
-for file in *.vcproj; do
-  echo "downgrading $file..."
-  sed -i -re 's/Version="9.00"/Version="8.00"/g;' $file
-done
-
-# Yes, really, that's it.