Releasing Namecoin Core 0.13

[domob]

I think that we should head towards making an official release relatively soon, given that we haven't in quite some time. Bitcoin Core 0.13 is out, and I've just tagged a 0.13 Namecoin Core release candidate based on that release:

https://github.com/namecoin/namecoin-co ... c0.13.0rc1

It includes the code to temporarily disable the low-S-signature check, so that miners/clients with this version are able to fully relay and mine transactions created by the legacy 0.3.80 client. This will go away with the next version, but is a good compromise to keep supporting the client just a little longer before the last users can finally migrate.

The release candidate does not yet include a UI for managing names, but once the pull request is fully completed and merged, we can release a follow-up 0.13.1 or so.

All feedback is very welcome - testing, building binaries, comments on what we still need for the final release, and so on!