A large functional test is added that automatically generates random transactions which
exercise various aspects of the new rules, and verifies they are accepted into the mempool
(when appropriate), and correctly accepted/rejected in (Python-constructed) blocks.
Includes sighashing code and many tests by Johnson Lau.
Includes a test by Matthew Zipkin.
Includes several tests and improvements by Greg Sanders.
Adds a --descriptors option globally to the test framework. This will
make the test create and use descriptor wallets. However some tests may
not work with this.
Some tests are modified to work with --descriptors and run with that
option in test_runer:
* wallet_basic.py
* wallet_encryption.py
* wallet_keypool.py
* wallet_keypool_topup.py
* wallet_labels.py
* wallet_avoidreuse.py
