Github-Pull: PIVX-Project#1796
Rebased-From: acf757b

dc0ed71 [BUG][GUI] Don't append cold-stake records twice (random-zebra)
91adcd7 masternode: CalculateScore and GetBlockHash accessing to chainActive without cs_main fix. (furszy)
eeb112f GetMasternodeInputAge: Missing cs_main lock (furszy)
52ec12d refactor: decouple decompose coinstake from TransactionRecord::decomposeTransaction. (furszy)
51a8389 [BUG] Properly copy fCoinStake memeber between CTxInUndo and CCoins Github-Pull: #1796 Rebased-From: acf757b (random-zebra)
5c3caa4 lock cs_main for Misbehaving (furszy)
5c629d8 openssl.org dependency download link changed (CryptoDev-Project)
11aa63c Do not try to resend transactions if the node is importing or in IBD. (furszy)
c59b62e [Core] Remove BIP30 check (random-zebra)
3f05eba include missing atomic to make CMake linux happy. (furszy)
f0cfd88 Make the cs_sendProcessing a LOCK instead of a TRY_LOCK (Matt Corallo)
d38e28c Split CNode::cs_vSend: message processing and message sending (Matt Corallo)
7561b18 Remove double brackets in addrman (Matt Corallo)
63c629b Fix AddrMan locking (Matt Corallo)
f78cec4 Make fDisconnect an std::atomic (Matt Corallo)
ec56cf5 net: fix a few cases where messages were sent rather than dropped upon disconnection (furszy)
7697085 Acquire cs_main lock before cs_wallet during wallet initialization (random-zebra)
c796593 Remove bogus assert on number of oubound connections. (Matt Corallo)
7521065 wallet: Ignore MarkConflict if block hash is not known (random-zebra)
72042ac Move disconnectBlocks logging to use __func__ instead of hardcoded method name. (furszy)
0f66764 Simplify DisconnectBlock arguments/return value (furszy)
cca4a8c Split logic to undo txin's off DisconnectBlock (furszy)
0f883e6 Cleaner disconnectBlock flow for coinbase and zerocoin txs. (furszy)
a7cbc46 Move UndoWriteToDisk() and UndoReadFromDisk() to anon namespace (random-zebra)
de5a405 Decouple CBlockUndo from CDiskBlockPos (jtimon)
671143c Decouple miner.o and txmempool.o from CTxUndo (random-zebra)
9419228 Decouple CCoins from CTxInUndo (jtimon)

Pull request description:

  Backports the following PRs to the `4.2` branch:

  #1746
  #1735
  #1767
  #1769
  #1781
  #1780
  #1775
  #1783
  #1750
  #1785
  #1796
  #1776
  #1791

ACKs for top commit:
  furszy:
    Added #1805. utACK dc0ed71.
  random-zebra:
    utACK dc0ed71

Tree-SHA512: 0e59c9e751597b1b6f9a419e117946cec468dffdb921c882a44e5770ecb1a36b7d3d25f8c7f97d48bb3d59f136492842c08969901512d957a17bfaec6aece449

535d8e4 scripted-diff: various renames for per-utxo consistency (random-zebra)
60c73ad Rename CCoinsCacheEntry::coins to coin (Pieter Wuille)
1166f1f Merge CCoinsViewCache's GetOutputFor and AccessCoin (Pieter Wuille)
f25d3c6 [MOVEONLY] Move old CCoins class to txdb.cpp (random-zebra)
aab17b3 Upgrade from per-tx database to per-txout (Pieter Wuille)
a55eb98 Reduce reserved memory space for flushing (random-zebra)
7d637ea Remove unused CCoins methods (random-zebra)
4b7b1a3 Extend coins_tests (random-zebra)
8cf2dc0 Switch CCoinsView and chainstate db from per-txid to per-txout (random-zebra)
b20a662 [Cleanup] Remove unused CCoinsViewCache::IsOutputAvailable (random-zebra)
ea82855 Refactor GetUTXOStats in preparation for per-COutPoint iteration (Pieter Wuille)
0f9f2b6 [Core] Fix not-pruned-check in miner for zerocoin mint outputs (random-zebra)
3698d47 Replace CCoins-based CTxMemPool::pruneSpent with isSpent (Pieter Wuille)
11c728a Remove ModifyCoins/ModifyNewCoins (Pieter Wuille)
3c65936 Switch tests from ModifyCoins to AddCoin/SpendCoin (random-zebra)
b05fe55 Switch CScriptCheck to use Coin instead of CCoins (random-zebra)
9e5c2ae Only pass things committed to by tx's witness hash to CScriptCheck (random-zebra)
22b0b4a [Cleanup] fix warning in comparisons with nCoinbaseMaturity (random-zebra)
666081d Switch from per-tx to per-txout CCoinsViewCache methods in some places (random-zebra)
53fc2be [Core] PIVX: remove potential_overwrite: BIP34 has always been enforced (random-zebra)
16924aa Introduce new per-txout CCoinsViewCache functions (random-zebra)
2d74bc1 Optimization: Coin&& to ApplyTxInUndo (random-zebra)
3fcb092 Replace CTxInUndo with Coin (random-zebra)
42a8996 [Core] PIVX: Add fCoinStake boolean field to Coin class (random-zebra)
a01a9f2 Introduce Coin, a single unspent output (random-zebra)

Pull request description:

  The chainstate database, and its cache, rely on a per-tx model (i.e. it is a map from txids to *lists* of unspent outputs).
  This PR chages it to a per-txout model (i.e. a map from outpoints to *single* unspent outputs).

  Pros:
  - Simpler code.
  - Avoiding the CPU overhead of deserializing and serializing the unused outputs.
  - More predictable memory usage.
  - More easily adaptable to various cache flushing strategies.

  Cons:
  - Slightly larger on-disk representation, and sometimes larger in-memory representation (when there are multiple outputs for the same txid in the cache, which becomes optional).

  Adapted from bitcoin#10195 (adding a `fCoinStake` boolean memeber to the Coin class and considering BIP34 always in effect as per #1775)

  Based on top of:
  - [x] #1799
  - [x] #1800
  - [x] #1797
  - [x] #1796
  - [x] #1795
  - [x] #1793
  - [x] #1773

  The actual PR starts with "Introduce Coin, a single unspent output" (171bf0b8a55de0e3f94305b33e97bb1cf4a01b70)

  ⚠️  **Note for testers**: Do a backup of the chainstate before testing. With this PR, at startup, the database is automatically upgraded to the new format (so a reindex is not needed).

ACKs for top commit:
  furszy:
    Code review ACK 535d8e4. Need some live testing now.
  furszy:
    ACK 535d8e4
  Fuzzbawls:
    ACK 535d8e4

Tree-SHA512: 8648d31c343ff901f8568c14d0848241c9b8aca0b9a8f89f3e5dbe02d384ba35faf572757e84f979fba1f198d721a2516d0e784b5e0dc8d02b6e308b4278b484