Trigger BIP65 and BIP66 based on the hight of the tip rather than the hight of the block being connected

Summary:
This continues the work started in D1262 .

Depends on D1262

Test Plan:

make check
./test/functional/test_runner.py --extended

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Subscribers: teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1263