rules:  fixes and cleanups

- Unify `./configure` for run-time and kpkg builds
  - Fix `$(KSRC)` default
  - Conditionally build dummy RTAI `.config` in run-time pkg builds
  - Set `RTAI_INSTALLDIR` and `RTAI_LINUXDIR` config from commandline
- Update files going into `rtai-source` tarball
- Remove a bunch of cruft
- Readability fixes
  - Wrap lines for readability
    - before I go blind
  - Organize `install` target by package
  - Move kernel build targets together at end of file