group_info and use it to store both, along with a count for each.
Cache group info on a per-user basis using getgrouplist() to get
the groups. We no longer need special to special case the user or
list user for user_in_group() and thus no longer need to reset the
groups list when listing another user.
Set adminstrative domain for the process when looking up user's
password or group info and when preparing for execve().
Include strings.h even if string.h exists since they may define
different things. Fixes warnings on AIX and others.
