t4118: avoid sed invocation on file without terminating newline

Some versions of sed exit non-zero if the file they are supplied is not newline terminated. Solaris's /usr/xpg4/bin/sed is one such sed. In this case the sed invocation can be avoided entirely since the resulting file is equivalent to a previously created file. So, just copy that file into place instead. Signed-off-by: Brandon Casey <casey@nrlssc.navy.mil> Signed-off-by: Junio C Hamano <gitster@pobox.com>