This will make a number of things easier in the future, as well as (finally!)
avoiding the Id-smashing problem which has plagued developers for so long.
Boy, I'm glad we're not using sup anymore. This update would have been
insane otherwise.
also add the missing declaration of forkpty() to libutil.h.
Btw., the calling interface for login(3) is crude. Some better
abstraction is needed, perhaps similar to logwtmp(3).
2.2 candidate, but i'll wait for the spelling police first. :)
