patch 9.0.1100: a hashtab with many removed items is not cleaned up

Problem:    A hashtab with many removed items is not cleaned up.
Solution:   Re-hash a hashtab even when the size didn't change if too many
            items were removed.

src/version.c

@@ -695,6 +695,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1100,
 /**/
     1099,
 /**/