Infernalist and Druid changes

Infernalists have received three new spells - void infusion, shared agony
and enslaved summoning. As part of this addition, we will soon be removing
access to the other nephandi racial spells that were inadvertently made
accessible in the creation of prestige. We waited to make this change
until these new abilities were ready.

Void infusion and agony should be working well, while the new demon friend for
infernalists may require some adjustments with field testing.

Infernalists also now have their own helpfile. Thanks to Gonnil for the code
on shared agony and enslaved summoning.

For druids, the formula for dorn nadur has been adjusted to be mana dependent.
The result of this new formula will be an improvement for standard druids but
a much needed decrease for prestige druids. The original prestige formula for
dorn nadur, like the original formula for grasp, has been determined to be too
powerful. This change will help regular druids and give both prestige and
regular druids access to a scalable damage spell.

On an equipment note for druids, the war staff of the elemental wizard has
also been adjusted. Fire storm will be cast less frequently by the weapon and
the average damage has been decreased.