[crossfire] Bugfix to prevent the server from damaging spells in player's inventories

[Andreas Kirschbaum]

I just committed a bugfix that prevents spells in player's inventories
from getting damaged. The most visible effect of these damaged spells is
the spell remove curse. If damaged, it always says "You are not using
any cursed items." even if you are wearing a cursed item.

My patch will not fix already damaged spells in player's inventories, it
just prevents the server from damaging newly learned spells. From my
testing, that bug affects at least the following spells:

  spell_armour
  spell_bless
  spell_charisma
  spell_constitution
  spell_curse
  spell_detect_curse
  spell_detect_magic
  spell_dexterity
  spell_holy_possession
  spell_protection_from_xxx
  spell_remove_curse
  spell_strength

To fix a player's inventory it should be sufficient to remove all
additional fields from spell_xxx (and probably abil_xxx) entries. For
example, a damaged spell looks like

  arch spell_remove_curse
  cursed 0
  end

but a working one looks like

  arch spell_remove_curse
  end