Problems with unstable
======================
Solved, or having a known solution:
- It is clear when a module depends on an unstable module
  via the "unstable" keyword in place of the version number
- unstable package repositories could be rejected from the
  "main" SLUL package repo(s).


To be solved:
- How to make it clear, for the person building the module, that it has an
  unstable API, or that it depends on another module with an unstable API?
    - a flag to cslul? --allow-unstable/-u ?
    - a marker in the output filename?   e.g. helloworld-unstable