This maintains BC with the old string-based system.
* src/validate/ValidStateMonitor.js (_getCause): Added.
(detectFixes): Consider failure cause if available when checking for fixes.
This is to facilitate a transition to Failure without a BC break.
* test/validate/ValidStateMonitorTest.js: Ensure that replacing messages
with Failure will continue to operate as expected.
The intent is to ultimately replace ClientFieldValidator with this and
individual validators that interact with it.
* src/validate/ValidStateMonitor.js: Added
* test/validate/ValidStateMonitorTest.js: Added