t4118: avoid sed invocation on file without terminating newline

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>