This will cause undesired behavior on future.get(), as
it will throw an ExecutionException, wrapping the internal
exception.
The response object will be inaccessible.

Revert "fix issue #84 https://github.com/koush/ion/issues/84"

This reverts commit f0cf95baa0e333298919ba4e9db1a01ae5ff50ef.
TransformFuture: remove from, and use "then".