t7600: use test_write_lines()

In t7600, we were rewriting `printf '%s\n' ...` to create files from
parameters, one per line. However, we already have a function that wraps
this for us: test_write_lines(). Rewrite these instances to use that
function instead of open coding it.

Signed-off-by: Denton Liu <liu.denton@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t7600-merge.sh

@@ -29,15 +29,15 @@ Testing basic merge operations/option parsing.
 . ./test-lib.sh
 . "$TEST_DIRECTORY"/lib-gpg.sh
 
-printf '%s\n' 1 2 3 4 5 6 7 8 9 >file
-printf '%s\n' '1 X' 2 3 4 5 6 7 8 9 >file.1
-printf '%s\n' 1 2 3 4 '5 X' 6 7 8 9 >file.5
-printf '%s\n' 1 2 3 4 5 6 7 8 '9 X' >file.9
-printf '%s\n' 1 2 3 4 5 6 7 8 '9 Y' >file.9y
-printf '%s\n' '1 X' 2 3 4 5 6 7 8 9 >result.1
-printf '%s\n' '1 X' 2 3 4 '5 X' 6 7 8 9 >result.1-5
-printf '%s\n' '1 X' 2 3 4 '5 X' 6 7 8 '9 X' >result.1-5-9
-printf '%s\n' 1 2 3 4 5 6 7 8 '9 Z' >result.9z
+test_write_lines 1 2 3 4 5 6 7 8 9 >file
+test_write_lines '1 X' 2 3 4 5 6 7 8 9 >file.1
+test_write_lines 1 2 3 4 '5 X' 6 7 8 9 >file.5
+test_write_lines 1 2 3 4 5 6 7 8 '9 X' >file.9
+test_write_lines 1 2 3 4 5 6 7 8 '9 Y' >file.9y
+test_write_lines '1 X' 2 3 4 5 6 7 8 9 >result.1
+test_write_lines '1 X' 2 3 4 '5 X' 6 7 8 9 >result.1-5
+test_write_lines '1 X' 2 3 4 '5 X' 6 7 8 '9 X' >result.1-5-9
+test_write_lines 1 2 3 4 5 6 7 8 '9 Z' >result.9z
 
 create_merge_msgs () {
 	echo "Merge tag 'c2'" >msg.1-5 &&
@@ -81,7 +81,7 @@ verify_head () {
 }
 
 verify_parents () {
-	printf '%s\n' "$@" >parents.expected &&
+	test_write_lines "$@" >parents.expected &&
 	>parents.actual &&
 	i=1 &&
 	while test $i -le $#
@@ -95,7 +95,7 @@ verify_parents () {
 }
 
 verify_mergeheads () {
-	printf '%s\n' "$@" >mergehead.expected &&
+	test_write_lines "$@" >mergehead.expected &&
 	while read sha1 rest
 	do
 		git rev-parse $sha1