Copy `_notificationHandlers ` in case it was mutated while being enumerated
Merge pull request #804 from dismory/master

Copy `_notificationHandlers ` in case it is mutated while being enumerated
Update changelog for #804
Handle object cycles in -description by limiting the recursion depth
Merge pull request #798 from realm/tg-description-cycle

Handle object cycles in -description.
Add more and better tests for link queries
Implement BETWEEN for link queries
Implement the IN operator for link queries
Add a helper for checking predicate preconditions
Extract some duplicate code for ORing queries