xenmon: Fix security vulnerability CVE-2007-3919.
The xenbaked daemon and xenmon utility communicate via a mmap'ed
shared file. Since this file is located in /tmp, unprivileged users
can cause arbitrary files to be truncated by creating a symlink from
the well-known /tmp filename to e.g., /etc/passwd.
The fix is to place the shared file in a directory to which only root
should have access (in this case /var/run/).
This bug was reported, and the fix suggested, by Steve Kemp
<skx@debian.org>. Thanks!
Signed-off-by: Keir Fraser <keir@xensource.com>