Add setresuid/4,5

alcove is usually called from sudo which sets uid, euid and suid
appropriately. However, if run with the setuid bit, the behaviour might
be more mysterious as shown in "Setuid Demystified":

http://www.usenix.org/events/sec02/full_papers/chen/chen.pdf

setresuid(2) is a more predictable interface. But of course it is not
supported by Solaris.