Use getnameinfo() to get canonical IPv6 addresses

Use getnameinfo() to get canonical IPv6 addresses

* protect mapRejectedBlocks by cs_main

* few block reprocessing fixes:
- DisconnectBlock should fail on DisconnectTip failure
- ResolveConflicts should fail on DisconnectBlock failure
- ReprocessBlocks cleanup

* don't ban on IsBlockValueValid/IsBlockPayeeValid failure

* Add rpc feature: reconsidermostworkchain

This feature is intended to be used during fork testing but also
for node operators which have fogotten to upgrade their clients before
a fork.  Getting back on to the correct fork can be a problem if there
have been a few blocks mined on the old chain after the fork time. By
running this command the chain will automatically rollback to the forkpoint
and then join the most work chain.

* Add tests to blockchain.py for reconsidermostworkchain

* fix up logging in blockchain.py

* update help text for reconsidermostworkchain

* return with message that nothing was done if we are already on the correct chain

* Make sure that if the test silently fails that we assert

…take class

b77c064 [Docs] Document zerocoin-related RPC changes for release notes (random-zebra)
4800729 [Core][Cleanup] Remove modifier as member of StakeInput objects (random-zebra)
238ea5f [Core][Cleanup][zPIV] CZPivStake --> CLegacyZPivStake (random-zebra)
f1b21a2 [Core][Cleanup][zPIV] Remove code to produce v2 spends and zPOS stakes (random-zebra)

Pull request description:

  This removes (now unused) code to produce old zerocoin spends and zPOS stakes.
  `CZPivStake` class is replaced with a `CLegacyZPivStake` (moved in new files `zpiv/zpos.*`) used exclusively to validate the chain.
  This also refactors `CStakeInput` class, removing the modifier functions (put back in kernel) and cleans up `kernel.*` files, removing old code and reorganizing them.

  This PR is based on top of:
  - [x] bitcoin#1259
  - [x] bitcoin#1290

  and it will be rebased after their merge. Only last **3** commits are relevant

ACKs for top commit:
  furszy:
    Re-acking the PR, release notes added. ACK b77c064
  Fuzzbawls:
    ACK b77c064

Tree-SHA512: cdf937822b435d3d05a8d3000d17340c74f7b7b17da4f1937935cb7bd71fddea9628c35a934c5abeea9ecb40b8daed074a49040479138a28fcd6699f2ca8bb8d

… proofs

29c02c7 [Cleanup] Remove ZerocoinParams from legacy CoinSpend classes (random-zebra)
a038651 [zPIV][Cleanup] Remove old CoinSpend proofs files (random-zebra)
26f407a [Cleanup][zPIV] Remove Acc Witness (random-zebra)
0052be4 [Cleanup][zPIV] Start removing old/unused zerocoin spend validation code (random-zebra)

Pull request description:

  Based on top of bitcoin#1291 .

  Old (v2) `CoinSpend` proofs are no longer checked. We can thus remove most of `AccumulatorProofOfKnowledge`, `SerialNumberSignatureOfKnowledge`
  and `CommitmentProofOfKnowledge`.
  We save only the structure and serialize methods (inside `CoinSpend.h`) to be able to parse them from the chain.

ACKs for top commit:
  furszy:
    ACK 29c02c7
  Fuzzbawls:
    ACK 29c02c7

Tree-SHA512: f4198443bf760fb398badff5bb31579bb0feb97677bbd55b23a136c07e35d3150588883ef7645f9f6122a0bbf394180d78012916e9bff41597756666945106ab

fe39b11 [Docs] Document change to the output of getblock RPC (random-zebra)
9aa29f1 [Cleanup] Remove un-needed modifier checkpoints map (random-zebra)
1504bf9 [Tests] Use V2 stake modifiers on regtest (issue bitcoin#1309) (random-zebra)
3ad11a7 [RPC] Add stakeModifier to getblock verbose output (random-zebra)

Pull request description:

  Based on top of bitcoin#1291 .
  Closes bitcoin#1309

ACKs for top commit:
  Fuzzbawls:
    utACK fe39b11
  furszy:
    utACK fe39b11

Tree-SHA512: 599d558cfff2ed0306984a4375c37cdcd75897a8b04ceae31da955b382328e442676b872a797e7d4fe60993e23e8e660567fee26d561c563d2be76155d1de3cf