* Store the native representation directly in the `ExitStatus` structure instead
of a "parsed version" (mostly for Unix).
* On Windows, be more robust against processes exiting with the status of 259.
Unfortunately this exit code corresponds to `STILL_ACTIVE`, causing libstd to
think the process was still alive, causing an infinite loop. Instead the loop
is removed altogether and `WaitForSingleObject` is used to wait for the
process to exit.
