NH4: Disallow changing to explore mode during a game

Disallow changing to explore mode during a game
Alex Smith <ais523@bham.ac.uk>
74dea97f1a7e2bca91a78b1ba37928ca6f423d6e
NH4: Formally ID wands if engraving gives a unique message

Credit to Christian Stegen.

Formally ID wants on engrave-ID, if it's obvious
Alex Smith <ais523@bham.ac.uk>
1e341842b09f3a8714f64ee6a97a5bfd85e91070
NH4: Don't merge unnamed items with named items

The only valid reason for unnamed items to ever merge with named items
was to cater to zen conduct players keeping informally BUC-ID'd stacks
of items like potions and scrolls, which has been addressed by
BUC-stacking in an earlier commit.  This conflicted with the far more
common use of item naming: to prevent items from stacking with each
other.

This is extracted from a commit in NetHack4.

AceHack-style item stacking
Alex Smith <ais523@bham.ac.uk>
0df7237f3af5a40d594bbac4fbb6e701b85dd18c
Don't put background colors behind monsters

Make sure hostile monsters are clearly visible even if they're on object
piles or stairs, which is the same behavior as on NAO.
Don't echo bogus coordinates when cancelling a position prompt

Pressing escape when choosing a location/position now shows "<position:
cancelled>" instead of "<position: (xx, yy)>" where xx and yy didn't
correspond to anything meaningful.

This bug also exists in NetHack4.
Allow hitting with polearms and lances in melee

Their weight and mediocre damage are enough incentive to consider other
weapons; not allowing them in melee made them useless in any dark place,
which describes 80% of the game.
Allow spellcasting if hands are stuck to a quarterstaff

This gives spellcasters slightly more incentive to use staffs.

Stuck hands is a really dumb mechanic in general, considering it blocks
spellcasting and container use (where you always keep holy water and
scrolls of remove curse), and prayer never works in Gehennom.  The
NetHack DevTeam's response to this is a new #tip command, but they
haven't released anything for a decade.  However, GruntHack has a
working implementation of exactly this command, which I'll probably end
up porting here at some point.