DATAMONGO-949 - CycleGuard should only match properties in word boundaries.

We modified the regular expression used for cycle detection to match on the exact property name within the inspected path using word boundaries. This fix prevents sub sequences of an existing property (like ‘sub’ would have matched ‘substr’) from being matched.

Along the way we fixed the (false) assertion in one of the tests, as we create the +1 cycle reference index before actually breaking the operation.