Nudge up the chance of a primary vault placing in Zot.

In particular, the chance that any one level in Zot:1-4 will get a
primary vault is 33%, equivalent to D:20-23's chance.

I've brought this up elsewhere, and the only major concern seems to be
that if we place a really large amount of primary vaults Zot will get
bogged down in stair vaults; this is thus a significantly more modest
increase than has been suggested elsewhere.
Stop dropping lines from the message window due to an extra (nasal) -=.

(Yes, I'm pretty sure this -= was causing undefined behaviour.)
Add a comment to message_window::reset_temp().
Some thrashing horror changes

Thrashing horrors are no longer living creatures, as this was
inconsistent with other Abyssals and had odd interactions with
god goods, particularly after they frenzied (TSO would object to
you killing them, for example). They are now nonliving like the
rest. Additionally, they now use might at low hp instead of frenzy,
since turning neutral often resulted in them attacking nothing at
all. Finally, they lose see invis (it felt a little odd for an
unintelligent mound of thrashing flesh to have this)
Fix wtile: not working on anything other than shields.
More bludgeon butchery: allow knife use as long as the form can wield.

(Don't worry about pesky things like "are there any limbs left with
which to wield the knife?".)
Disable energy randomization for allies following the player.

Like f542eec, it doesn't serve much other purpose than traffic jam.
Remove an Ashenzari overflow altar

It no longer makes sense with butchery restrictions removed.
Comment fix
Remove a reference to orb mimics

Since we no longer have alternate orb chambers.
Fix beam name "force bolt" implying that the bolt is a beam

In other cases, "bolt" (bolt of foo, venom/lightning bolt, etc) implies
a penetrating beam, which striking is not.
Remove a reference to ball lightnings casting spells
Fix okawaru_arena trapping players

Hatches let pacified monsters leave the vault, as well as letting the
player escape if something else goes wrong somehow. Also prevent the
iron trees from being disintegrated (you still lose Fedhas piety for
shattering them though, probably they should just be normal trees).

This vault still causes crashes, see #6846.
Remove a pair of abyss vaults

Their idea of "wretched stars behind grates" doesn't actually function.
Add PURE/IMMUTABLE to many functions in itemprop.h and refine a few types.
Remove unneeded "if (artefact)" checks from auto-ID code for jewellery.

I needed them gone for some experiments I was doing, and they don't
really do anything useful anyway ...