v3.8.7-beta.9

Support explicit 'UnknownUser' unauthenticated access (#1888)

Companion to intersystems-community/intersystems-servermanager#366,
which makes "username": "UnknownUser" request unauthenticated access.

- Use BasicAuthorization and the corrected spec types from the
  3.15.0-beta.3 package instead of a local copy.
- Skip the Authorization header when it is empty.
- On a 401 for UnknownUser, report the rejection instead of asking for
  a password.
- Compare intersystems.servers changes against getServerSpec, so
  recording UnknownUser doesn't reconnect.
- Document UnknownUser in the objectscript.conn schema.
- Test UnknownUser for each connection kind. The '-anonymous' cases
  also accept UnknownUser, since Server Manager may record it during a
  run.