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.