I've finally gotten 'cpio' into a shape where it could be useable.
This version can archive and extract directories, sockets, FIFOs, devices,
symlinks, and regular files.
Supported options are -iot, -H FMT (which is a dummy right now).
It only writes newc, and could read newc or newcrc.

This does NOT implement -d, which essentially is equivalent to
mkdir -p $(dirname $FILE)
for every file that needs it.
Hard links are not supported, though it would be easy to add them given
a hash table or something like that.
I also have not implemented the "<n> blocks" output on stderr.
If desired, I can add it pretty simply.

There is one assumption this makes: that the mode of a file, as mode_t,
is bitwise equivalent to the mode as defined for the cpio format.
This is true of Linux, but is not mandated by POSIX.
If it is compiled for a system where that is false, the archives will
not be portable.
Teach scripts/test.sh to call scripts/single.sh.
Prep work for useradd by Ashwini Sharma.
Minor lib/password.c cleanup, described on the list. (Inline two functions.)
useradd, groupadd, and mkpasswd submitted by Ashwini Sharma.