o Delay setuid() in srun with --uid until after nodes are allocated

   to specified user.
 o New srun option --no-shell
 o Changed uid/gid_from_name () to uid/gid_from_string () and allow
   either user/group name or numerical user/group ID.
 o updated srun(1) documentation with new --no-shell option and
   changed semantics for --uid.