On the revision:

- Make the .vers and .expsym files prerequisites of the libs type target.

- Canonicalize the license in the package manifests.

- Fix the switch statements in the buildfiles, replacing 'switch $c.class,
  $tsys' with 'switch $c.class'.

- Replace the C++ comments with C comments in tests.

On the release:

- Use legal{} target type for legal documentation (LICENSE, AUTHORS, etc).

  Note that this requires bumping build2 version requirement to 0.13.0.