Suggestions to clarify documentation for bind-chroot

(Me again!)

I was deploying with bind-chroot, and noticed an interesting scenario: if `bind-chroot` is installed and the zones file are copied to `/var/named/chroot/var/named` before `named` is started - it will fail to start (because `named` expects the destination to be empty so it can `mount --bind /var/named /var/named/chroot/var/named` and now a few of those default zone files like `named.ca` aren't present.)

Therefore, I thought that the documentation should be updated to reflect this, so I'm proposing the following changes:
- Don't suggest people deploy directly to /var/named/chroot/var/named
- Add a small explanation of the difference of older versions of BIND which you might get if you don't use the latest packages in RHEL5.

Thanks,
Jay