Merge pull request #1625 from takluyver/i1622 Fix deepreload on Python 3. As described in #1622, it seems that `imp.find_module()` on Python 3.2 imports other modules, like `io`, while running. We don't want deepreload to catch those, so this restores the original import hook for `find_module`. It's not terribly neat, but I don't currently see a better way of doing it. Ideally, we'd just delay installing our `__import__` until after `find_module` had run, but our implementation of `__import__` can itself call `find_module`, so this little dance seems to be necessary. Closes gh-1622.