[crossfire] New feature for scrolls and spellbooks

[Nicolas Weeger (Laposte)]

Hello.

Just implemented the feature request: add blessings and curses to scrolls
More details here: 
https://sourceforge.net/tracker/index.php?func=detail&aid=656191&group_id=13833&atid=363833

(that was the ancestor of all feature requests, may it rest in peace)


The effects I made are:

For scrolls:
* a cursed/damned scroll will do a random spell failure, at least mana drain 
or worse
* a blessed one has a 10% chance of not turning to dust

For spellbooks:
* a blessed spellbook gives +5 level for learning the spell
* a cursed/damned will make a random scroll failure
* a damned has a 20% chance of making the player forget the spell

Note that those cursed/damned/blessed can appear in shops too - should 
probably be fixed.

Also, price isn't adapted for blessed scrolls.


Parameters like probability or apparition & such should probably be adapted, 
too.

Nicolas