- sparc64: switch to 2.6.12 kernel; make CD multiboot 2.6 and 2.4,
using 2.6.12 by default
- sparc32: drop 2.6 kernel support as it has no 2.6.12 kernel
- restructure silo.conf with proper support for install, expert and
rescue boot options
Only enable the rescue isolinux targets for etch.
I hope at least some of the etch stuff (like tools/boot/etch) can be used
for the daily CD builds that build using d-i daily builds.