Fix new trap weights

Copy-paste error.
Add a monster gen flag MG_FORBID_BANDS to override MG_PERMIT_BANDS.

Because in some situations (place:foo for example) MG_PERMIT_BANDS may
be added even if we really want only one monster.

Currently unused.
Turn a vector into a static array.
Not so static (PleasingFungus, doh)

The contents change between calls of course.
Let XP-charged evokers stack in inventory.

When dropping an evoker from a stack, you will always drop the evoker that
will take the longest to charge from the stack.

Thanks to PleasingFungus for suggesting the general approach to take in
implementing this, and for some commentary and clarification that has
been squashed into this commit.
Give item_info evoker_debt as number of inerts in a stack (|amethyst).

Since the change in the original commit actually removed this info
entirely, unlike what was intended.
Merge dropped XP evokers into floor stacks properly (|amethyst).

Not handling this properly was causing the number of inert evokers
dropped into a stack to balloon unexpectedly.
Don't overwrite evoker_debt on partial pickup of a stack (|amethyst).

Instant recharging of evokers ahoy...
Don't "upgrade" white imps to shadow/iron in Call Imp

Old frequencies at low (0-46) and high (92, near the cap of 100)
spell power:

          low    high
Crimson  20/36  10/36
White    10/36   5/36
Shadow    4/36  14/36
Iron      2/36   7/36

New frequencies at the same power levels:

          low    high
Crimson  20/36  10/36
White    10/36  10/36
Shadow    4/36 ~11/36 (actually 8/27)
Iron      2/36  ~5/36 (actually 4/27)

The breakpoint at 47 power (when shadow/iron imps start to become more
common) is still there.
Fix invisible goblin tossing bugs
Trade Ironheart Preserver defenses for HP

Having better defenses than their pals (or even defenses that
were as good!) meant that the player was encouraged to prioritize
the pals first, generally killing the preserver indirectly
(through the injury bond) without ever bothering to interact with
them. A monster that the player shouldn't bother to attack is a
terrible, terrible design.

More hp means that they can actually soak up the damage the player
deals to their pals, and worse defenses mean that you can do more
HP damage by attacking them than their allies.
Tweak Preservers further

Better Minor Healing, worse armour.
Remove some errant rims

Someday, somehow, we shall reach that golden land wherein we never have to
fix %rim lines ever again.