diff-no-index: replace manual "."/".." check with is_dot_or_dotdot()

Helped-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Brian Bourn <ba.bourn@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff-no-index.c

@@ -15,6 +15,7 @@
 #include "log-tree.h"
 #include "builtin.h"
 #include "string-list.h"
+#include "dir.h"
 
 static int read_directory_contents(const char *path, struct string_list *list)
 {
@@ -25,7 +26,7 @@ static int read_directory_contents(const char *path, struct string_list *list)
 		return error("Could not open directory %s", path);
 
 	while ((e = readdir(dir)))
-		if (strcmp(".", e->d_name) && strcmp("..", e->d_name))
+		if (!is_dot_or_dotdot(e->d_name))
 			string_list_insert(list, e->d_name);
 
 	closedir(dir);