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/read.c

@@ -1693,7 +1693,7 @@ seffect_charging(struct obj **sobjp)
             else
                 u.uen = u.uenmax; /* otherwise restore current to max  */
         }
-        gc.context.botl = 1;
+        display.botl = 1;
         return;
     }
     /* known = TRUE; -- handled inline here */