rules:  'make test' prints KPKG_SUBARCH

Used in .config selection
rules:  add useful info to test target
Fix .config target to generate kernel configs with kconfigtool.py

- Add FLAVOR_CONFIG_FILE variable pointing at xenomai config
  - Run 'debian/rules test' to see its value
- Be sure that  .cofig isn't copied from anywhere weird in modules.mk
- Run kconfigtool from common.mk
Add two targets debian/stamp/xeno_{un,}patch to apply/remove xenomai patch

Workflow is to unpack the vanilla kernel, check out the debian
directory, and run dpkg-buildpackage.  Patch should be added
automatically.

Maybe the remove patch is hackish.