Make the MP and HP regeneration of !ambrosia independant

Before, the exact number of "points" regenerated (ex. 3 hp/mp) was
shared between the MP and HP regeneration. This was an odd and
unintuitive connection, so now the MP and HP regeneration independently
choose a number between 3-5.
Refactor _get_random_armour_type() (makeitem.cc)
Remove a weird special case in _get_random_armour_type()

This is technically an intentional mechanical change, but the difference
in armour type generation is imperceptibly small.
Refactor _abyss_place_vaults() (abyss.cc)
Assign vampires their spell frequencies (reaverb).

GGGRRRUUUNNNTTT
Improve Crawl's party potential

In the Book of Party Tricks, swap Blink for Invisibility.

Even out their respective rarity somewhat.
Fix monster cloud resistance checks (ebering)

Monsters were checking is_fiery() or is_icy() instead of their
actual resistances for purposes of fire/cold cloud immunity.
Fix robe ego odds

Accidently skewed by fa193e0f; among other things, odds of
Archmagi more than doubled.
Actually fix robe ego odds

Oops
Improve comments in _get_random_armour_type() (|amethyst)
Move _get_random_armour_type()

Mostly to avoid having to prototype it.
Make a comment clearer (PleasingFungus, |amethyst)

[ci skip]
Rename some Gozag constants for clarity.
Orange rat -> hell rat.

They're now demons, like hell hounds/hogs.
Simplify stabbing when not using a short blade.

The extra damage that a one-handed polearm or long blade got were never
really meaningful in practice. The same is true of clubstabbing; it was a
good joke, but clubs are such a weapon of last resort (or first, in
practice) that you'd never run into it.

Everything in the removed middle tier got bumped down to the normal stab
multiplier, except for felid claws, which moved to short blade (but not
dagger) effectiveness.
Remove most race-based special cases in starting gear.

With clubstabbing gone, there's no reason for OgEn/As to start with a
club. They have really bad short blades apts, sure, but that's true of
plenty of other starts. With them having short blades, --Hu also gets
the same short sword on all starts.

The only remaining special case is DrFi's armour, since it is completely
unable to use scale mail.
Improve tree-door interaction (#9299).
Confiscate Maurice's time machine (#9309).
Fix reversed dagger stabbing logic.
Smooth dodging penalties from armour

Wearing armour gives two separate penalties to EV. There's the AEVP penalty,
which scales with strength, armour skill, and the square of armour base EVP.
This is the component that can give you "negative" EV when in very heavy
armour. There's also a linear EVP penalty (with a formula that apparently
dates back to 4.1...?), which scales with strength, armour base EVP, and
size.

The latter penalty is the problem one - since it's capped by Dodging skill,
it makes Dodging do nothing until you "overcome" the penalty, at which
point Dodging gives EV at the same rate as if you had no armour at all.
This is misleading for new players (since it looks for all the world as
if Dodging is completely useless when in heavy armour) and rather clunky
beside.

This changes the linear penalty to divide EV from dodging rather than
subtracting from it. This makes heavy armour better at low Dodging and
worse at high Dodging; or, in other words, makes small amounts of
Dodging investment useful for heavy armour users, but high levels of
Dodging less of a priority. Which seems reasonable.

Some example values are here: http://pastebin.com/nKt9dqJH .