extend softfork test to cover the hard fork flag

[arvidn]

This is to test the cases where we make the new operators available outside the softfork-guard.

We make sure they fail with "unknown operator" in mempool mode, and are treated as unknown in consensus (i.e. return NIL).

When the hard fork flag is set, we ensure they work as expected in both mempool and consensus mode.

[coveralls-official]

Pull Request Test Coverage Report for Build 9095271893

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 94.162%

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Totals
Change from base Build 9086294840:	0.0%
Covered Lines:	5806
Relevant Lines:	6166

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💛 - Coveralls

[Rigidity]

A bit confusing to read at first, but makes sense now - lgtm