Turn conjuration-type monster special abilities into spells instead.

Since there's no reason for them to be abilities now that their
frequency of use can be controlled well.

This contains some incredibly ugly hacks to get Fedhas oklob spit
frequency to still scale with invocations / oklob HD properly. A better
solution would be welcome.
Don't let all monsters cast Dig.

WWWHHHEEEAAALLLSSS
Give SPELL_DRACONIAN_BREATH to nonbase draconians.

...allowing the removal of a lot of side code for nonbase draconian
breath.

Also give Tiamat her breath back.
Turn some more mon-abils to spells.

Battlecry, Signal Horn, Seal Doors, and Flay.

Battlecry could use some improvements; it's still very monster-specific
right now. (Perhaps it could be split into three spells?)

(Time to give Flay to Gloorx Vloq?)
Remove M_FAKE_SPELLS (Grunt).

It was used by nothing important at this point.
Give ice dragons ice breath.

GRUUUUUUUUUNT
Replace M_NOISY_SPELLS with a slot flag.
Remove the (basically) unused monster spell flags.

If you have the actual monster to check, then you should look at its
slots to see whether it's an actual spellcaster or priest, now. The class
flags were not removed since they are potentially useful if you don't
have an actual instance of that monster.

Fixes a bug where godless monsters could not polymorph into dual-wielding
monsters.
Unbrace / simplify.