EXN_STACKTRACE should contain nested exceptions

[pmconrad]

Quite often, higher-level code wraps exceptions thrown by lower-level code into their own exceptions. The stacktrace of the wrapping exception then only contains the higher-level location where the wrapping exception was thrown, not the lower-level location where the original exception happened.
Usually logging appenders resolve this problem by showing the wrapped exception and some of its stacktrace below the trace of the wrapping exception, separated by a "Caused by..." line (or similar).
It would be good to have this here, too.