Order of locks in optimistic locking is not strict

In OptimisticLockingInterceptor, the keys are ordered according to their hash. However, the hashes can still collide, which may result in a deadlock if two keys with identical hash (only 32-bit) are sorted to different order. We should try to check if the keys are Comparable or let user provide some comparator class in config, and use the compare of hash only as the last resort.
In all cases, a warning should be emitted if the compare operation had non-strict result.