- FutureProxy may throw an exception directly from iteration via "FutureIterator" (see PHI1764). This is wrong: futures should throw only when resolved.
- FutureProxy can not change an exception into a result, or a result into an exception, or an exception into a different exception. Being able to proxy the full range of result and exception behavior is useful, particularly for Conduit (see PHI1802).
Make "FutureProxy" more robust in how it handles exceptions from proxied futures.