In order to automatically run unit tests with newly created
amendments, prefer to start with jtx::supported_features() and
then subtract unwanted features.
These changes identified a few bugs that were hiding in
amendments. One of those bugs, in FlowCross, is not yet fixed.
By uncommenting the test in CrossingLimits_test.cpp you can see
failures relating to that bug. Since FlowCross is not yet
enabled on the network we can fix the bug at our convenience.