[IRCServices] Feature: nickchange and guestnickprefix

[Alexander_Zverev at oxy.com]

> >I think than this feature is already implement. I just ask to do it 
> >more frexible.
> 
>      I agree, this is useless flexibility.  It also adds 
> complications in that Services has to check whether the new 
> randomly-generated nick is registered (GuestNickPrefix nicks 
> are not allowed to be registered so they don't have this problem).

Services prevent randomly-generated nick registration, that start with
CuestNickPrefix and only that nicks, but they _doesn`t_ prevent
registration for randomly-generated nicks (flood registration).
Therefore any restrictions, than comes with GuestNickPrefix, are
useless, isn`t it?