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.

src/music.c

@@ -706,7 +706,7 @@ do_improvisation(struct obj* instr)
             Hero_playnotes(obj_to_instr(&itmp), improvisation, 50);
         }
         awaken_monsters(u.ulevel * (mundane ? 5 : 40));
-        gc.context.botl = TRUE;
+        display.botl = TRUE;
         break;
     default:
         impossible("What a weird instrument (%d)!", instr->otyp);