replace /var/run and /var/lock. For instance, udev now keeps state
in /run/udev instead of /dev/.udev. See
http://lists.fedoraproject.org/pipermail/devel/2011-March/150031.html
http://bugs.freestandards.org/show_bug.cgi?id=718
So this patch creates /run as a tmpfs, and symlinks /var/run to /run
and /var/lock to /run/lock.
TODO: create /run in stage 1 and propagate it to stage 2.
svn path=/nixos/trunk/; revision=27803