bundle the display-related hints, that tell bot() and others

that an update is required, into a struct. Remove it from
context since there is no reason to save those.

include/context.h

@@ -159,8 +159,8 @@ struct context_info {
     boolean move;
     boolean mv;
     boolean bypasses;    /* bypass flag is set on at least one fobj */
-    boolean botl;        /* partially redo status line */
-    boolean botlx;       /* print an entirely new bottom line */
+    boolean placeholder1;
+    boolean placeholder2;
     boolean door_opened; /* set to true if door was opened during test_move */
     boolean tips[NUM_TIPS];
     struct dig_info digging;