> It looks like the build core dumped on Travis-CI

I failed to account for the extra stuff left on the stack when handling exceptions and jumping out of a finally block due to a `break`. Caught by Serhiy's tests in https://github.com/python/cpython/pull/5078.
I could add a work around, but it would be a bit hacky.

I'm now convinced that code duplication is the only way to do this properly. The only real advantage of JSR-style finally blocks is the ease of implementation of `frame.set_lineno()`.

Rather than go around in circles any more, I suggest that we merge Serhiy's PR (PR 5006). I can then cherry-pick my commits to clean up the implementation of the `with` statement (as a new PR).

I then plan to implement `try-finally` using code duplication, but that might not make it into 3.7 and we shouldn't hold up this issue any longer.