Count OP_CHECKDATASIG and OP_CHECKDATASIGVERIFY as sigops when the proper flag is set.

Summary:
As per title. Once the opcode activates, it needs to count as a sigops.

Depends on D1601

Test Plan: Added test cases.

Reviewers: #bitcoin_abc, schancel, jasonbcox

Reviewed By: #bitcoin_abc, schancel, jasonbcox

Subscribers: jasonbcox, teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1605