Implement getpwname(), setuid() and setgid() in the simplest way possible
considering that we don't support any userid except 0:

getpwname() returns user 0 for any username given to it.
setuid() and setgid() does nothing for uid or gid 0, otherwise fails.
Where would the caller get this !=0 id anyway?

Memcached needs these calls, because it wants to be clever and
warn the user against running it as root....