RFC: bitcoinconsensus.h: Introduce new function to accept UTXO amount

[afk11]

This adds an error bitcoinconsensus_ERR_AMOUNT_REQUIRED, when bitcoinconsensus_verify_script is called with the witness bit set. Normal usage will feed the amount 0 into VerifyScript.

Adds bitcoinconsensus_verify_with_amount(), which takes the usual arguments and the amount.

To facilitate future changes, I've added a static function to accept all parameters and flags. Also bumps the version constant (exposed via bitcoinconsensus_version())

I modified a test which touched this function also:

• if the witness flag is set, only bitcoinconsensus_verify_script_with_amount() is called.
• Otherwise, we test both methods - passing a value of zero as the amount since the old sighash algorithm will be used.

[sipa]

Can you squash?

[afk11]

Done

[sipa]

Merging.