[crossfire] Group spells

[Nicolas Weeger]

Hello.

I committed a few days ago a new spell type, 48, 'party spell', which
lets a player cast a spell on party members in the same map.
It will need to be throughly tested, I'm not sure whether everything
works or not, or if behaviour is as intended :)
To make one such spell:
* define subtype as 48
* fill in 'other_arch' with the spell archetype

Note that spell uses party spell's statistics for gp/sp, not party
spell, and has a one-time cost.
Also currently all players on the same map are affected, for the same
price, whereas maybe it could be decided randomly or based on distance.

Ryo