_x11 user and group for the X server when run by xdm. ok deraadt@

The actual X code to use them will be added soon.

src/etc/group

@@ -21,6 +21,7 @@ guest:*:31:root
 _rusersd:*:32:
 _fingerd:*:33:
 _sshagnt:*:34:
+_x11:*:35:
 utmp:*:45:
 crontab:*:66:
 www:*:67:

src/etc/master.passwd

@@ -10,6 +10,7 @@ _identd:*:29:29::0:0:identd:/var/empty:/sbin/nologin
 _rstatd:*:30:30::0:0:rpc.rstatd:/var/empty:/sbin/nologin
 _rusersd:*:32:32::0:0:rpc.rusersd:/var/empty:/sbin/nologin
 _fingerd:*:33:33::0:0:fingerd:/var/empty:/sbin/nologin
+_x11:*:34:35::0:0:X server:/var/empty:/sbin/nologin
 uucp:*:66:1::0:0:UNIX-to-UNIX Copy:/var/spool/uucppublic:/usr/libexec/uucp/uucico
 www:*:67:67::0:0:HTTP server:/var/www:/sbin/nologin
 named:*:70:70::0:0:BIND Name Service Daemon:/var/named:/sbin/nologin