Move nBits check to ContextualCheckBlock

[aguycalled]

This PR moves the nBits check to ContextualCheckBlock.

[proletesseract]

Travis failed, re-running

[mxaddict]

utACK

[mxaddict]

@aguycalled I think reindex.py test fails on this branch

[aguycalled]

It passed locally

$ ./qa/pull-tester/rpc-tests.py reindex.py
WARNING: "import zmq" failed. Set ENABLE_ZMQ=0 or to run zmq tests, see dependency info in /qa/README.md.
.....................................................................................
reindex.py:
Initializing test directory /var/folders/qh/7_l8lmqx2sb5ncxgtzzyb51r0000gn/T/testjsjz8dit/0
Success
Success
Success
Success
Stopping nodes
Cleaning up
Tests successful

 
Pass: True, Duration: 43 s

TEST       | PASSED | DURATION

reindex.py | True   | 43 s

ALL        | True   | 43 s (accumulated)

Runtime: 43 s

Restarting travis

[mxaddict]

@aguycalled maybe you should merge master into this PR?

[mxaddict]

testedACK

[mxaddict]

testedACK

Tested on Ubuntu 18.04

[proletesseract]

building and testing now

[proletesseract]

Compiles and runs on ubuntu 18.04.

• The --reindex flag gets stuck as best block 229 for me. Reconsidering the block doesn't get past it.
• The --reindex-chainstate flag also gets stuck as best block 229 for me. Reconsidering the block does get past it though.
• Removing the data folder and syncing again gets past block 229.

Assuming this is just some localised problem and am still happy to merge, just thought it was worth documenting what happened in my tests.

Tests pass on travis so haven't run them locally.