Improve guild attitudes script functions

[thokkat]

In wld_getguildattitude the order of guilds is wrong. Attitude from second guild to first is returned instead of first to second.

In wld_setguildattitude two attitudes are set but in vanilla it's only the first.

I fixed the above, expanded bounds checking and unified names. In wld_exchangeguildattitude every attitude is now only set once instead twice.