[DGD] Hydra 1.3.13

[Felix A. Croes]

I've released Hydra 1.3.13.  It catches up with DGD 1.6.4, and includes
a fix for the crash-on-exit problem reported for version 1.3.12.

Note that it is not completely snapshot-compatible with the previous
version.  I am currently tweaking the runtime VM to prepare it for
just-in-time compilation, and 1.3.13 supports only the most current
incarnation; I do not want to slow down Hydra with supporting a
variety of VM versions.

As soon as the VM stabilizes, Hydra will start being backward compatible.
In the meanwhile, use DGD to convert snapshots.

Regards,
Felix Croes