Support Bitcoin Cash Nov 2018 HF

[svyatonik]

Details: bitcoincashorg/bitcoincash.org#94

• Remove topological transaction order constraint, and enforce canonical transaction order (see this paper). Notes: affects mining code.
• Enable OP_CHECKDATASIG and OP_CHECKDATASIGVERIFY opcodes (see this document)
• Transactions that are smaller than 100 bytes shall be considered invalid
• Enforce "push only" rule for scriptSig (rule#2 in this BIP)
• Clean Stack (rule#6 in this BIP)
• Automatic Replay Protection (https://github.com/bitcoincashorg/bitcoincash.org/blob/master/spec/may-2018-hardfork.md#automatic-replay-protection)