Prevent wanderers from wielding 2h + shield.

Added a few checks to newgame_make_item to prevent this. I only did the
minimum required to prevent this bug - it could reappear if exotic
wanderer items are added.
Store the summoner in struct monster.

Nothing queries it yet -- the blame chain uses a string resolved at monster creation time.
Store battlesphere's owner in monster.summoner.
Store IOOD's caster in monster.summoner.
Store spectral weapon's owner in monster.summoner.
Set boring stat mutation probabilities to zero.

MUT_STRONG_STIFF and MUT_FLEXIBLE_WEAK probabilities are hereby
set to zero in preparation for removal.
Remove an obsolete spell description.
Don't crash on p{ghost,illusion,anlord} xv (#7514)
Make stat mutations less boring.

Replace 14 levels of stat mutations with 2.
Each tier conveys +/-2.
If a player happened to have +14 strength, for example,
convert the excess strength to base strength.
Be conservative in converting bad stat mutations to avoid
splatting players.
Formatting fixes
Revamp Stone of Tremors

Of the revised elemental evokers, the stone was definitely the least-used
and least useful; it required both the player and their targets to be
adjacent to the same wall and didn't work at all with stone or permarock,
further limiting the places it could operate. And for all that, its damage
output was often less than the lamp of fire and provided little further
utility.

Instead of its old effect, the stone now causes rubble to fall from all
rock, stone, or permarock walls within the player's LoS, damaging anything
adjacent to these, regardless of where the player is standing (it will not
hit your own location, however). Additionally, the chance of shafting
monsters has been increased somewhat and does not require them to be adjacent
to a wall, either.
Reduce elemental evoker power (especially at low evocations)

While I'm overall happy with the new evokers, I feel like they're a bit
too effective with next to no investment in evocations (and thus have
become something that nearly every character wants to have along with
them). This commit is aimed at making them a little worse with low
evocations without reducing their power by much at higher evocations.

The thresholds to get a second and third elemental have been raised (and
by extension, a second and third flame trail from the lamp of fire). The
power of the phial's primal wave have been reduced a bit at lower evocations,
and the HD scaling of water and especially fire elementals have been reduced,
as the latter in particular benefited much more from it than the other
elementals due to its AF_PURE_FIRE melee. However, impact damage of the lamp
has been slightly increased, and minimal cloud duration raised slightly.
Aside from the elemental thresholds, the fan of gales is untouched.
Reduce the recharge rate bonus from high evocations for elemental evokers

With high evocations skill in lategame, it was common for an elemental
evoker to recharge only a battle or so after being used, which I feel
is more quickly than intended.

I still feel like the recharge formula is wonky and could use work, but
it seems to be overall in a better place since the general xp changes.
Experimentally revamp scrolls of immolation

Scrolls of immolation are around the most purposeless scrolls in the game
at the moment. They're supposedly double-edged, yet don't do enough damage
to virtually ever be useful offensively (even if they didn't hurt the player
at the same time), and are deliberately generated deep enough that it's
incredibly unlikely any player will kill themselves with one (not that it
would be particularly good design if this was untrue). Nearly all the time,
one will read-ID it in a safe place, take some piddling damage, and then
never pick up or read another for the rest of the game. Worse, they're a
hazard to read around allies (either turning Yred servants hostile, or
angering Beogh and all your horde directly), encouraging tedious behavior
of sending all your allies away whenever you read-ID, until you have found
?immolation.

Instead of their old effect, ?immolation now enchants all susceptible monsters
in LoS with inner flame. This does include friendly monsters, but this does
not anger them or your god, meaning that there is no longer any need to
repeatedly send allies away before read-IDing scrolls. I hope that inner flame
will also convey the supposed double-edged intent of the scroll better than the
original, by granting a potentially powerful and useful effect that also has a
non-negligible risk of getting the player caught up and injured in it. For some
characters, I can even see these being rather good (rarity and such can
be adjusted if they are too much so, of course).
Reduce default Inner Flame duration to something more sane

The old duration ranged from 75 to 125 turns, which was rather extreme
(and often harmful and annoying to the caster, since if you fail to kill
the hexed enemy in a short span of time, probably they are in your face
and you would LIKE it to wear off instead of lasting forever.)

It now only lasts 25-35 turns, which is still a decent bit, but less
excessive.
Make lost souls less attracted to extremely high HD creatures

The considerable gap between ancient lich HD and the HD of any other
high-tier Crypt threat meant that every lost soul would always be attracted
to them and only them, should one be on the level. HD is now capped for
purposes of this effect, which should better spread the lost souls among
other high-end threats on the level, even if an ancient lich is also present.
Decrease Lost Soul speed and hp slightly
Describe M_FAKE_SPELLS as "special", not "magical" abilities.
Move spells to the end of the monster description (dpeg)

And pull the logic out into a separate function for readability.
Increase enchantment on weapon randarts.

It was generally agreed that weapon randarts are a bit weaker than non-weapon
randarts on average. This commit buffs them by increasing their accuracy and
damage enchantment by about 3 each on average (while maintaining the same
[-6,+12] range of possibilities).