Update for NetBSD 6.1.

- remove objcopy for sh3el since a raw GENERIC.bin kernel is available in 6.1
- fetch cdrtools packages binary directly during executing Makefile on dcburn
- also fetch a GENERIC.bin kernel in dcburn Makefile
- use sh(1)'s $(()) expressions rather than expr(1)
- bump version
Update README files for 6.1 version.