patch 9.0.0906: mouse scroll code is not optimal

Problem:    Mouse scroll code is not optimal.
Solution:   Properly organise Normal mode, Insert mode and common code.
            (Christopher Plewright, closes #11572)

src/version.c

@@ -695,6 +695,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    906,
 /**/
     905,
 /**/