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: NBrandon Casey <casey@nrlssc.navy.mil>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

t/t4118-apply-empty-context.sh

@@ -23,7 +23,7 @@ test_expect_success setup '
 	cat file2 >file2.orig &&
 	git add file1 file2 &&
 	sed -e "/^B/d" <file1.orig >file1 &&
-	sed -e "/^[BQ]/d" <file2.orig >file2 &&
+	cat file1 > file2 &&
 	echo Q | tr -d "\\012" >>file2 &&
 	cat file1 >file1.mods &&
 	cat file2 >file2.mods &&