string_list: Add STRING_LIST_INIT macro and make use of it.

Acked-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Thiago Farina <tfransosi@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/diff-no-index.c b/diff-no-index.c
index 43aeeba..ce9e783 100644
--- a/diff-no-index.c
+++ b/diff-no-index.c
@@ -64,7 +64,8 @@
 
 	if (S_ISDIR(mode1) || S_ISDIR(mode2)) {
 		char buffer1[PATH_MAX], buffer2[PATH_MAX];
-		struct string_list p1 = {NULL, 0, 0, 1}, p2 = {NULL, 0, 0, 1};
+		struct string_list p1 = STRING_LIST_INIT_DUP;
+		struct string_list p2 = STRING_LIST_INIT_DUP;
 		int len1 = 0, len2 = 0, i1, i2, ret = 0;
 
 		if (name1 && read_directory(name1, &p1))