ENG-3633: Improve constraint violation error logging in the easiest
possible way.  ConstraintFailureException already has all the info we
care about; override message() to generate a useful string.
Also:
- Address namespace pet peeve
- Add CONSTRAINT_TYPE_PARTITIONING to constraintutil::getNameForType()
- Make construction of ConstraintFailureException() use
  consistent calling convention for new/previous tuple argument order.
Merge pull request #624 from VoltDB/eng3633

ENG-3633, r=jhugg