../../common/Makefile.mdset supports building multiple copies of the
same kernel (as long as they're to separate filenames).
Now there's no need to set FLOPPYKERNDIR, as it now defaults to instkernel.
single and multi-volume floppies in better fashion that the crufty
shell commands in the various Makefiles.
- Move fdset* -> bootfloppy*, as that's more consistent
dsl