lstat_cache(): swap func(length, string) into func(string, length)

Swap function argument pair (length, string) into (string, length) to
conform with the commonly used order inside the GIT source code.

Also, add a note about this fact into the coding guidelines.

Signed-off-by: Kjetil Barvik <barvik@broadpark.no>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/diff-lib.c b/diff-lib.c
index a41e1ec..a3ba20e 100644
--- a/diff-lib.c
+++ b/diff-lib.c
@@ -31,7 +31,7 @@
 			return -1;
 		return 1;
 	}
-	if (has_symlink_leading_path(ce_namelen(ce), ce->name))
+	if (has_symlink_leading_path(ce->name, ce_namelen(ce)))
 		return 1;
 	if (S_ISDIR(st->st_mode)) {
 		unsigned char sub[20];