sound distribution practices

[Allison Randal]

Patrick and I just chatted on the phone, here's a summary of the working
scenario we reached:

- Rakudo will deliver a Rakudo release for each supported ("stable")
Parrot release, a few days after the Parrot release.

- Debian will package each supported release of Parrot.

Debian packages for Rakudo will either:

- Rebuild the old Rakudo packages on the new Parrot packages (since the
old compiled bytecode, etc won't work on a different version of Parrot), or

- Package the new version of Rakudo at exactly the same time as the new
version of Parrot. Define the version requirements so tightly (=) that
the Rakudo packages require exactly one version of Parrot.

The first alternative is better, and will be the first preference. But
it needs stable APIs from Parrot, so old Rakudo packages consistently
work on newer versions of Parrot. This is mostly working, but the
exceptions are pain points for packaging (we've got one coming up for 4.3).

Allison