patch 8.1.1493: redrawing with popups is slow and causes flicker

Problem:    Redrawing with popups is slow and causes flicker.
Solution:   Avoid clearing and redrawing using a zindex mask.
diff --git a/src/version.c b/src/version.c
index d1ef98b..fb159d9 100644
--- a/src/version.c
+++ b/src/version.c
@@ -768,6 +768,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1493,
+/**/
     1492,
 /**/
     1491,