stick gtest to r629


git-svn-id: http://protobuf.googlecode.com/svn@538 630680e5-0e50-0410-840e-4b1c322b438d
Change MemoryBarrier() to MemoryBarrierInternal(). Resolve name conflict in mingw gcc 4.8.1


git-svn-id: http://protobuf.googlecode.com/svn@539 630680e5-0e50-0410-840e-4b1c322b438d