Introducing Ushabti, guardian mummy dilution for Tomb

Guardian mummies, the main fodder in Tomb, are awkward if functional designs.
Slow, melee-only amassed monsters with a punishing effect for killing them has
obvious value in countering mass conjurations, but a few will go to great
lengths to avoid or diminish their effects through, say, luring seperation
tactics or the previous summoning effect. Some of this is arguably due to
the psychological damage of statdrain, rot, and lighter draining amounts,
which, while repairable concepts each and of themselves (plus eventually
replacable), are also only used in any serious amounts in this branch anyway.
This suggests an attempt to dilute rather than replace the death curse bombs
known as guardian mummies.

The ushabti, more light ancient Egyptian lore, are funerary figurines intended
to serve as workers and servants for the dead in the afterlife. Their
introduction cuts into the appearance rate of guardian mummies by 2/5s.
They're non-living, have stats not very far away from guardian mummies but
with more resists, and provide more flavour / non-demonic non-undead placements
for extended. While they're still push-overs for when they appear alone,
especially since they're still slow like guardian mummies, they've got two
tricks that should make them rather relevant in Tomb:

 * Loud shouts, louder than dragon roars (The ushabti rumbles deeply! x6).
   Obviously relevant in the quietness of Tomb, and considering the monster
   use possibly a replacement enough of it.
 * A new spell, "Death Rattle". This breathes a line of randomly-mixed miasma
   and draining clouds, similarly to the petrifying breath of catoblepae.
   They don't cast it too often, though a little more when at low health:
   the movement this suggestions to avoid clouds with effects close to the
   lighter death curses should be a rather interesting incarnation of the
   intent of guardian mummy death curses, considering how often one is pinned
   down in Tomb.
Death scarabs.

A swarming undead insect that trails miasma and bites to drain life,
speed, or skill.

The combination of miasma trails and fast batty movement is intended to
interfere with player movement unless they're dealt with quickly.

The exact set of AF_SCARAB effects could probably be adjusted; right now
it feels like too much of a duplicate of other Tomb effects.
Monster spell: Summon Scarabs, for a greater mummy spell set.

This particular set has Summon Emperor Scorpions and two instances of
Summon Scarabs for the full insect swarm effect.
Anubis guards.

They are intended to sereve a similar purpose / threat level to guardian
mummies in Tomb while being more than a "walking death curse bomb".

They are living enemies with rN+++ and torment immunity (flavoured as
being conditioned to ignore extreme amounts of pain), and are equipped
with draining breath, Hunting Cry (effectively a signal horn that also
alerts other anubis guards on the level to your location on a one-off
basis), Dispel Undead (have to keep the unruly denizens in line
somehow), and Confuse (ditto). When they are generated randomly (i.e.
outside of vaults) they have a 50% chance of coming as a pair.

Weights of guardian mummy slots in Tomb are now 1/6 guardian mummies,
1/6 death scarab bands, 1/3 ushabti, and 1/3 anubis guard bands. These
may need further reweighting.
Tiles for the new enemies.
Increase anubis guard Dispel Undead frequency.

Playtesting on a few devs' part suggests they weren't dispelling enough
previously, meaning they weren't consistently a threat to undead
players.

This doubles the frequency, which may be too much - but better to err on
the side of killing more players, I say.
Adjust frequencies of replacement of Tomb guardian mummies.

Each vault/subvault now picks one of three replacement sets for the
glyphs formerly corresponding to guardian mummies - one each for
ushabtiu, anubis guards, and death scarabs - and there is code in place
to ensure an even frequency distribution between the three of them on a
per-vault/subvault basis.
Redistribute random guardian mummy replacement generation weights, too.

This is a really rough reportioning, but it should work decently.
Increase probably of death scarab bites having side effects.

In particular, the draining effects should happen more consistently.
Re-tuned brightness for many floor tiles

The same dynamic from light to dark has been preserved in every tile, but shifted downward in value. This should make several areas with noisy floors less aggravating, and will improve visibility of most other tiles in the game.
Cull idempotent misc items from shopping lists (#8873)
dc-floor.txt mostly caught up to new floor tiles.

Also one floor tile that I mixed up.
The only thing left to fix is to get %lum working for the pebble tiles.
Fix luminosity of pebble floor tiles

I just got it working; the actual lum. values can be changed later.
Fixup some debug messages.
Make anubis guards' quarterstaves visually distinctive in tiles.

As far as I can tell, the equip tile for this isn't actually in use
anywhere else, and it makes for a good visual explanation of why they're
wielding staves to begin with.
Fix @ delay display for sling bullets (9086)
Brighten the death scarab tile a bit.

The legs still blend into the floor somewhat, but it is more visible in
general.
Buff scarab bites further by adding a negative vulnerability effect.

A scarab bite now has the following:

1) 50% chance of inflicting rN- if the target does not already have it;
2) one of drain life or drain speed;
3) vampiricism.

rN- increases susceptibility to draining effects just as with other
negative resistances. Notably, a target with rN- can be killed by
torment.
Merge branch 'tombfodder'

The monster designs are at a point where I feel further tinkering can be
done in trunk. Thus, time to torment the players and figure out what
needs tinkering.
Hastily sneak an item image in that was missed in a previous commit.