Resolves Issue #49 -- bad fdspawned-interact()

tested on centos using script by @aidanhs, not that doing your own
pty.fork() is really recommended if you're going to use interact

Otherwise, tested also using traditional use of interact, though
that worked fine previously -- it still works fine, now.  With
this, the test script provided by aidnhs now exits fine.

I would be interested in a test case and a more precise use-case.
In my opinion, needs more study before acceptance.