NetHack has historically had problems (both in terms of interface
and in terms of gameplay exploits) caused by unidentified items
not stacking with identified items. The 3.7 change to cause items
picked up by monsters to become unidentified has exacerbated this,
e.g. there's an undesirable strategy in which players give
ammunition to hostile monsters in order to unidentify it, allowing
it to stack with other unidentified ammunition so that the whole
stack can be enchanted with a single scroll.
This commit makes it possible to stack items with different
identification statuses (unles Blind), in effect causing the
unidentified items to be identified by comparing them to the
identified items (this is consistent with the mechanic via which
two stacks of unidentified items can be determined to be the same
as each other). The hope is that this will prevent any gain from
exploits involving intentionally unidentifying (or intentionally
failing to identify) items, that it will prevent interface clutter
caused by (e.g.) a Ranger's main projectiles becoming partially
unidentified as a nymph picks them up and subsequently failing to
stack, and that it will reduce the incentive to backtrack to an
altar to merge, e.g., a stack of formally-known-uncursed and a
stack of informally-known-uncursed food rations to stack.
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