Check for sizeof(long long) right at the beginning of this test and
exit immediately if we're not on a 64-bit platform.  The previous
behavior here I think would still have been broken on a 32-bit
machine.



git-svn-id: svn://svn.r-forge.r-project.org/svnroot/rprotobuf@769 edb9625f-4e0d-4859-8d74-9fd3b1da38cb