Add test case for GetTransactionSigOpCount without the P2SH flags passed in.

Summary:
This is an untested code path.

Depends on D1595

Test Plan:

make check

Modify GetTransactionSigOpCount to always count P3SH sigops, make sure the test fails.

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Subscribers: teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1596