[sugar] How to handle application protocols

[J.M. Maurer]

While fixing some bugs in AbiCollab, I found a bug that I can only fix
by breaking the existing protocol. I can also imagine that this will
happen more in the future (caused by new features, or other unknown bugs
that might need fixing).

Do we have any policy on application level protocol changes? At the
moment, a "new" AbiCollab will simple refuse to communicate with an
"old" AbiCollab.

Cheers,
  Marc