Add a checkpoint for block 24480

[cjepson]

No description provided.

[chappjc]

tACK mainnet:

[INF] CHAN: Verified checkpoint at height 440/block 0000000000002203eb2c95ee96906730bb56b2985e174518f90eb4db29232d93
[INF] BMGR: Downloading headers for blocks 441 to 24480 from peer decred.monkeyland.io:9108
[INF] BMGR: Verified downloaded block header against checkpoint at height 24480/hash 0000000000000c9d4239c4ef7ef3fb5aaeed940244bc69c57c8c5e1f071b28a6
[INF] BMGR: Received 24040 block headers: Fetching blocks

And then the usual processing of blocks.... I guess I thought this would accelerate the process that follows, but it's about the same.

[alexlyp]

tACK

[alexlyp]

@chappjc I've noticed a pretty hefty sync speed increase with this and #189

Things will still be relatively slow for sync until we get in the other upgrades in btcd. But hopefully those will be in soon (with @davecgh speeding along with the sync)

[chappjc]

@alexlyp I don't have #189. Perhaps that's the difference.