t6023-merge-file: Work around non-portable sed usage

OS X sed doesn't understand '\n' on the right side of a substitution.
Use a valid substitution character instead and use 'tr' to convert
those to a newline.

Signed-off-by: Arjen Laarhoven <arjen@yaph.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t6023-merge-file.sh

@@ -150,8 +150,8 @@ test_expect_success 'MERGE_ZEALOUS simplifies non-conflicts' '
 
 '
 
-sed -e 's/deerit./&\n\n\n\n/' -e "s/locavit,/locavit;/" < new6.txt > new8.txt
-sed -e 's/deerit./&\n\n\n\n/' -e "s/locavit,/locavit --/" < new7.txt > new9.txt
+sed -e 's/deerit./&%%%%/' -e "s/locavit,/locavit;/"< new6.txt | tr '%' '\012' > new8.txt
+sed -e 's/deerit./&%%%%/' -e "s/locavit,/locavit --/" < new7.txt | tr '%' '\012' > new9.txt
 
 test_expect_success 'ZEALOUS_ALNUM' '