e.g. <machine canonical='pc'>pc-0.11</machine>
* src/capabilities.c: output the canonical machine names in the
capabilities output, if available
* docs/schemas/capabilities.rng: add the new attribute
by running this command:
git ls-files -z | xargs -0 perl -pi -0777 -e 's/\n\n+$/\n/'
This is in preparation for a more strict make syntax-check
rule that will detect trailing blank lines.
