* autoload.cc: Add LoadDLLfunc statements for SetTokenInformation@16.

    * autoload.cc: Add LoadDLLfunc statements for SetTokenInformation@16.
        * cygheap.cc: Include security.h.
        * grp.cc (internal_getgrent): New function.
        (getgroups): Rearranged using `internal_getgrent' and the new
        `cygsid' class.
        * passwd.cc (internal_getpwent): New function.
        * sec_acl.cc: Use new `cygsid' class throughout.
        (acl_access): Use `internal_getgrent' instead of `getgrent'.
        * sec_helper.cc: Use new `cygsid' class throughout.
        (get_id_from_sid): Use `internal_getgrent' instead of `getgrent'.
        Use `internal_getpwent' instead of `getpwent'.
        * security.cc: Use new `cygsid' class throughout.
        * security.h: Move `MAX_SID_LEN' from winsup.h to here.
        Add extern declarations for `internal_getgrent' and `internal_getpwent'.
        (class cygsid): New class.
        * shared.cc (sec_user): Use new `cygsid' class.
        * syscalls.cc (seteuid): Try to set owner to user and primary group to
        current group in impersonation token before performing impersonation.
        (setegid): Try to set primary group in process token to the new group
        if ntsec is on.
        * uinfo.cc (internal_getlogin): Use new `cygsid' class.
        Try to set owner to user and primary group to current group in process
        token if the process has been started from a non cygwin process.
        (uinfo_init): Set primary group only if the process has been started
        from a non cygwin process.
        * winsup.h: Move define for `MAX_SID_LEN' to security.h.