Ability to concatenate ErrorSponges with their stacktraces.

[Rush]

Let's suppose a remote JS error has occured and we have just serialized it over the network. We most likely need to generate a new error locally. Naive approach is either re-throwing the remote error or re-throwing the local error and logging the remote one before hand.

Bluebird has a feature of concatenating stacktraces from multiple asynchronously run stacks, like so:
http://bluebirdjs.com/docs/api/promise.longstacktraces.html

ReferenceError: a is not defined
    at evenMoreInner (<anonymous>:6:13)
From previous event:
    at inner (<anonymous>:5:24)
From previous event:
    at outer (<anonymous>:4:20)
From previous event:
    at <anonymous>:3:9
    at Object.InjectedScript._evaluateOn (<anonymous>:581:39)
    at Object.InjectedScript._evaluateAndWrap (<anonymous>:540:52)
    at Object.InjectedScript.evaluate (<anonymous>:459:21)

It would be extremely useful feature to have the same capability for serialized stacktraces, to be able to concatenate let's say two ErrorSponges into one error.

It could then be logged into Bugsnag for a full overview what has transpired during an incident.