Reuse sighash computations across evaluation (rebase of #4562)

qa/pull-tester/rpc-tests.py

@@ -107,6 +107,7 @@
     'fundrawtransaction.py',
     'p2p-compactblocks.py',
     'segwit.py',
+    'sighashcache.py',
     # vv Tests less than 2m vv
     'wallet.py',
     'wallet-accounts.py',