Fix for an issue where the @Id annotation rules were not properly validated.

If an Entity containing an @Id annotation extends a MappedSuperclass without an @Id annotation, a RuleValidationException is thrown. This happens because the list of keys found when iterating through the Entity's annotations gets erased when each super class is evaluated.
Merge pull request #578 from makearl/MappedSuperclassFix

Fixed an issue where the @Id annotation rules are not properly validated