untangle processing of exceptions in stack

Currently, the exceptions in the stack are being handled in tandem. All the breadth-first type visiting is happening for each exception in the stack, then all the depth-first type visiting is happening. Each exception should be processed in turn.

Consider this case:

The following exception chain is thrown: E1 -> E2 -> E3 (where "X -> Y" means X is caused by Y). Also, E3S is a superclass of E3. Let's assume there are handlers for all four exception types for both traversal modes (breadth-first and depth-first).

The expected order of execution is as follows:

E3S handler in the breadth-first traversal mode
E3 handler in the breadth-first traversal mode
E3 handler in the depth-first traversal mode
E3S handler in the depth-first traversal mode

E2 handler in the breadth-first traversal mode
E2 handler in the depth-first traversal mode

E1 handler in the breadth-first traversal mode
E1 handler in the depth-first traversal mode

We process the exceptions in the stack in the order E3, E2, E1 because we assume the cause, E3 is the most important exception.