address #H5426 - inventory category selections

Report #5426 was classified as not-a-bug, but the underlying issue
can be improved.

For item selection where BUCX (bless/curse state) filtering is
supported (mostly for menustyle:Full, but there are a few actions
where Traditional and Combination handle BUCX too), 3.4.3 took the
union of object class and bless/curse state (so ?!B gave all scrolls
and all potions and every blessed item from other classes) but 3.6.0
changed that to the intersection (so ?!B gives blessed scrolls and
blessed potions, period).  Since gold is inherently not blessed or
cursed it has been getting excluded during intersection handling
when that includes BUCX filtering.  Report #5426 was from a player
who was used to choosing $X when putting newly acquired loot into a
container asking to have the old behavior reinstated.

The ideal fix would be to support both union ($ | X) and intersection
(?! & B), but implementation would be bug prone and the interface,
especially when done for menus, would be cumbersome.  Instead, this
adds new boolean option, goldX, to allow the player to decide whether
gold is classified as uncursed--even though it is never described as
such--or unknown.  The new-loot-into-container issued can be solved
either via $abcX, where abc lists all classes that have any X items
(when gold is included as one of the classes, its BUCX state is now
ignored for the current selection), or by setting the goldX option
and then just picking X for the types of items to put into the
container (or drop or whatever other action supports BUCX filtering).

The situations where menustyle:Full allows BUCX filtering during
object class specification and styles Traditional and Combination
don't should to be fixed (by extending BUCX support to Traditional
and Combination rather than removing it from Full, obviously).

include/flag.h

@@ -1,4 +1,4 @@
-/* NetHack 3.6	flag.h	$NHDT-Date: 1497479080 2017/06/14 22:24:40 $  $NHDT-Branch: NetHack-3.6.0 $:$NHDT-Revision: 1.118 $ */
+/* NetHack 3.6	flag.h	$NHDT-Date: 1498078871 2017/06/21 21:01:11 $  $NHDT-Branch: NetHack-3.6.0 $:$NHDT-Revision: 1.119 $ */
 /* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
 /* NetHack may be freely redistributed.  See license for details. */
 
@@ -217,6 +217,9 @@ struct instance_flags {
     boolean cbreak;           /* in cbreak mode, rogue format */
     boolean deferred_X;       /* deferred entry into explore mode */
     boolean echo;             /* 1 to echo characters */
+    /* FIXME: goldX belongs in flags, but putting it in iflags avoids
+       breaking 3.6.[01] save files */
+    boolean goldX;            /* for BUCX filtering, whether gold is X or U */
     boolean hilite_pile;      /* mark piles of objects with a hilite */
     boolean implicit_uncursed; /* maybe omit "uncursed" status in inventory */
     boolean mention_walls;    /* give feedback when bumping walls */