Thanks to @maaku for the updated tests

c5c92c4 Update python tests for default tx version=2 (BtcDrak)
dab207e Preserve tx version=1 for certain tests (BtcDrak)
c5d746a tiny test fix for mempool_tests (Alex Morcos)
1f0ca1a Bump default transaction version to 2 (BtcDrak)

This temporarily disables the upstream bump of the default tx version
(in bitcoin/bitcoin#7562) until we can catch up
with Namecoin on necessary updates.

It updates the code for the removal of external conflict tracking for
the mempool (bitcoin/bitcoin#9240), but we keep
the logic to track and report name conflicts as we have a separate
signal for them.

Finally, the change to name_registration.py is necessary due to
https://github.com/bitcoin/bitcoin/pull/9302/files, after which a
non-accepted tx to the mempool no longer fails the RPC but instead just
gets "silently" not added to the mempool.

Conflicts:
	src/Makefile.test.include
	src/bench/verify_script.cpp
	src/primitives/transaction.h
	src/test/data/bitcoin-util-test.json
	src/test/data/txcreate1.hex
	src/test/mempool_tests.cpp
	src/test/script_tests.cpp
	src/txmempool.cpp
	src/txmempool.h
	src/validation.cpp

This reverts commit 1f0ca1a. It breaks backward compatibility between BitZeny 1.1.x and 1.2.x. Don't forget to revert this commit again after the BIP68 softfork enforces.

ref.
bitcoin/bitcoin#7562

This reverts commit 1f0ca1a. It breaks backward compatibility between BitZeny 1.1.x and 1.2.x. Don't forget to revert this commit again after the BIP68 softfork enforces.

ref.
bitcoin/bitcoin#7562

This reverts commit 1f0ca1a. It breaks backward compatibility between BitZeny 1.1.x and 1.2.x. Don't forget to revert this commit again after the BIP68 softfork enforces.

ref.
bitcoin/bitcoin#7562

This reverts commit 1f0ca1a. It breaks backward compatibility between BitZeny 1.1.x and 1.2.x. Don't forget to revert this commit again after the BIP68 softfork enforces.

ref.
bitcoin/bitcoin#7562

This reverts commit 1f0ca1a. It breaks backward compatibility between BitZeny 1.1.x and 1.2.x. Don't forget to revert this commit again after the BIP68 softfork enforces.

ref.
bitcoin/bitcoin#7562

This reverts commit 1f0ca1a. It breaks backward compatibility between BitZeny 1.1.x and 1.2.x. Don't forget to revert this commit again after the BIP68 softfork enforces.

ref.
bitcoin/bitcoin#7562

This reverts commit 1f0ca1a. It breaks compatibility between BitZeny 1.1.x and 1.2.x. Don't forget to revert this commit again after the BIP68 softfork enforces.

ref.
bitcoin/bitcoin#7562

c5c92c4 Update python tests for default tx version=2 (BtcDrak)
dab207e Preserve tx version=1 for certain tests (BtcDrak)
c5d746a tiny test fix for mempool_tests (Alex Morcos)
1f0ca1a Bump default transaction version to 2 (BtcDrak)

c5c92c4 Update python tests for default tx version=2 (BtcDrak)
dab207e Preserve tx version=1 for certain tests (BtcDrak)
c5d746a tiny test fix for mempool_tests (Alex Morcos)
1f0ca1a Bump default transaction version to 2 (BtcDrak)

This reverts commit 21648e4.

9b9c616 Fix missing zapwallettxes mode in wallet_hd.py functional test (furszy)
d6d0ad9 [logs] fix zapwallettxes startup logs (John Newbery)
006c503 [wallet] fix zapwallettxes interaction with persistent mempool (John Newbery)
c6d45c6 Adapting and connecting mempool_persist.py functional test to the test runner. (furszy)
4f26a4e Control mempool persistence using a command line parameter. (John Newbery)
5d949de [Qt] Do proper shutdown (Jonas Schnelli)
e60da98 Allow shutdown during LoadMempool, dump only when necessary (Jonas Schnelli)
c0a0e81 Moving TxMempoolInfo tx member to CTransactionRef (furszy)
f0c2255 Add mempool.dat to doc/files.md (furszy)
8e52226 Add DumpMempool and LoadMempool (Pieter Wuille)
44c635d Add AcceptToMemoryPoolWithTime function (Pieter Wuille)
6bbc6a9 Add feedelta to TxMempoolInfo (Pieter Wuille)
9979f3d [mempool] move removed and conflicts transaction ref list to vector. (furszy)
4f672c2 Make removed and conflicted arguments optional to remove (Pieter Wuille)
e51c4b8 Bypass removeRecursive in removeForReorg (Pieter Wuille)
54cf7c0 Get rid of CTxMempool::lookup() entirely (furszy)
35bc2a9 Finished the switch CTransaction storage in mempool to CTransactionRef and introduced the timeLastMempoolReq coming from btc#8080. (furszy)
d10583b An adapted version of btc@b5599147533103efea896a1fc4ff51f2d3ad5808 (furszy)
cb4fc6c An adapted version of btc@ed7068302c7490e8061cb3a558a0f83a465beeea (furszy)
9645775 Split up and optimize transaction and block inv queues (furszy)
68bc68f Don't do mempool lookups for "mempool" command without a filter (furszy)
7624823 mapNextTx: use pointer as key, simplify value (furszy)
191c62e Return mempool queries in dependency order (Pieter Wuille)
23c9f3e Eliminate TX trickle bypass, sort TX invs for privacy and priority. (furszy)
6ebfd17 tiny test fix for mempool_tests (Alex Morcos)
8c0016e Check all ancestor state in CTxMemPool::check() (furszy)
91c6096 Add ancestor feerate index to mempool (Suhas Daftuar)
64e84e2 Add ancestor tracking to mempool  This implements caching of ancestor state to each mempool entry, similar to descendant tracking, but also including caching sigops-with-ancestors (as that metric will be helpful to future code that implements better transaction selection in CreatenewBlock). (furszy)
8325bb4 Fix mempool limiting for PrioritiseTransaction Redo the feerate index to be based on mining score, rather than fee. (furszy)
1fa40ac Remove work limit in UpdateForDescendants()  The work limit served to prevent the descendant walking algorithm from doing too much work by marking the parent transaction as dirty. However to implement ancestor tracking, it's not possible to similarly mark those descendant transactions as dirty without having to calculate them to begin with.  This commit removes the work limit altogether. With appropriate chain limits (-limitdescendantcount) the concern about doing too much work inside this function should be mitigated. (furszy)
ba32375 Rename CTxMemPool::remove -> removeRecursive  remove is no longer called non-recursively, so simplify the logic and eliminate an unnecessary parameter (furszy)
c30fa16 CTxMemPool::removeForBlock now uses RemoveStaged (furszy)

Pull request description:

  Ending up 2020 with a large PR :).

  Included a good number of performance and privacy improvements over the mempool and inv processing/sending areas + added mempool cache dump/load.
  Almost finishing with #1726 work, getting closer to 9725, and getting closer to be able to decouple the message processing thread <-> wallet and the wallet <-> GUI locks dependencies (which will be another long story.. but well, step by step).

  The final goal is clear, a much faster syncing process using pivx-qt (a good speed up for pivxd as well), smoother visual navigation when big wallets are syncing, less thread synchronization issues, among all of the improvements that will be coming with the backports adaptations.

  Adapted the following PRs to our sources:

  bitcoin#7062 —> only eb30666.
  bitcoin#7174 —> complete.
  bitcoin#7562 —> only c5d746a.
  bitcoin#7594 —> complete.
  bitcoin#7840 —> complete.
  bitcoin#7997 —> complete.
  bitcoin#8080 —> complete
  bitcoin#8126 —> except e9b4780 (we don't have the mapRelay) and c2a4724 (we don't have the relay expiration vector).
  bitcoin#8448 —> complete
  bitcoin#8515 —> complete
  bitcoin#9408 —> complete
  bitcoin#9966 —> complete
  bitcoin#10330 —> complete

ACKs for top commit:
  random-zebra:
    ACK 9b9c616
  Fuzzbawls:
    ACK 9b9c616

Tree-SHA512: 186bd09bbb19b55ec0d46dc27291663a0df2d60d8238c661a8c9b8cbf3677b6f8a92fa56bd7346a3cb5293712eeccc5d6542ee3c441d35a4f61e7d12e2ce489a