[chaincfg] Add a checkpoint at the next release.

[davecgh]

Since the chain is new and there is only roughly 2 TH/s hash power securing the network, I think it's important to get an initial checkpoint in place with the next release to prevent the ability to rewrite history before that point once more hash power shows up.

[jcvernaleo]

@davecgh @cjepson any thoughts as to a particular block to use for a checkpoint? I don't see any reason not to add one.

[davecgh]

The findcheckpoint utility exists for identifying good candidates. From that list, I usually just pick one that has a 0 on the end so it's a nice round number.

[jcvernaleo]

I totally forgot that findcheckpoint existed. I'll give that a shot and do a PR for this soon.

[jcvernaleo]

As we discussed on irc, this brought up some issues findcheckpoint (from the upstream btcd version) has when there are no existing checkpoints and when working early in the chain. So this will have to wait for those to be fixed.

[jcvernaleo]

@davecgh I can do a hash at:
Candidate 4 -- Height: 140, Hash: 000000000001cf214856cd2714479af5286c2b70160a21ae9babea7eea1f6311
Do you think that is worth it or should I wait until we are further in the chain?

[davecgh]

I think it would be worthwhile to wait to at least 257 so the initial coins have matured by the time the checkpoint is reached.