Adding Java causedBy support via shim frames

@brianr this isn't _exactly_ what we talked about, but we have had it on our ticket tracker for awhile, I took a crack at faking support for Java's `causedBy`/inner exceptions by appending them to the stack trace, and delimiting via 'shim' frames.

You can see the output of with vs. without the causedBy "support" via: https://gist.github.com/slpsys/de061536084c3809bb1c

Which is just something like:
`(report-exception token env (Exception. "test"))`
vs.
`(report-exception token env (Exception. "test" (Exception. "inner test")))`

Thoughts?