[crossfire] Ideas needed to fix exploit

[Andreas Kirschbaum]

It seems to me that the consensus is to base the exp gain of the
attacker on the exp loss of the victim. The amount should be settable in
the config file. A possible transferral of exp between skills is not
considered a problem.

That said, I think I'll add a new setting pk_exp_ratio which takes a
value between 0 (no exp gain for pk) and 100 (attacker gains all exp the
victim loses) with a default of 50.

The current code limits the exp gain to 5 million. Should I keep this
limit, or add just another settings variable (pk_exp_limit, defaults to
5 million)?