patch 8.0.0599: diff mode is insufficiently tested

Problem:    diff mode is insufficiently tested
Solution:   Add more test cases. (Dominique Pelle, closes #1685)
diff --git a/src/version.c b/src/version.c
index 700b4bd..a572ae3 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    599,
+/**/
     598,
 /**/
     597,