lost my r2xxxxx subversion id in uname & kern.version

[Dan Mack]

I'm not sure exactly when but recently I've lost the subversion id from 
kern.version and hence uname and motd.

Subsequent fresh rebuilds from source don't bring it back even after 
wiping out the tree.

Today it looks like this:

root at olive:~ # uname -a
FreeBSD olive.example.com 10.0-CURRENT FreeBSD 10.0-CURRENT #0: Fri 
Jul 12 19:38:24 CDT 2013 
root at olive.example.com:/usr/obj/usr/src/sys/MACKGEN  amd64
root at olive:~ # sysctl kern.version
kern.version: FreeBSD 10.0-CURRENT #0: Fri Jul 12 19:38:24 CDT 2013
     root at olive.example.com:/usr/obj/usr/src/sys/MACKGEN

Previously it would have '#0 r253307' in it's place.

This only happened on 1 of 3 build machines.

dan